refactor: migrate to kotlinx serialization, eliminate gson dependency

.idea/dictionaries/project.xml

@@ -7,12 +7,15 @@
       <w>Nostr</w>
       <w>Tink</w>
       <w>amboss</w>
+      <w>cltv</w>
       <w>hkdf</w>
       <w>inflight</w>
       <w>lnbc</w>
       <w>lnbits</w>
       <w>lnurlp</w>
       <w>msat</w>
+      <w>msats</w>
+      <w>nostr</w>
       <w>satoshis</w>
       <w>sats</w>
       <w>snackbar</w>

app/build.gradle.kts

@@ -17,6 +17,7 @@ plugins {
     alias(libs.plugins.kotlin.compose)
     alias(libs.plugins.ksp)
     alias(libs.plugins.protobuf)
+    alias(libs.plugins.kotlin.serialization)
 }
 
 android {
@@ -132,7 +133,7 @@ dependencies {
 
     // Networking
     implementation(libs.retrofit2.retrofit)
-    implementation(libs.converter.gson)
+    implementation(libs.converter.kotlinx.serialization)
     implementation(libs.okhttp)
     debugImplementation(libs.logging.interceptor)
 
@@ -163,7 +164,7 @@ dependencies {
     implementation(libs.androidx.biometric)
 
     // JSON
-    implementation(libs.gson)
+    implementation(libs.kotlinx.serialization.json)
 
     // icons
     implementation(libs.androidx.material.icons.extended)

app/src/main/java/com/bitcointxoko/gudariwallet/api/Adapters.kt

@@ -1,9 +1,16 @@
 package com.bitcointxoko.gudariwallet.api
 
-import com.google.gson.TypeAdapter
-import com.google.gson.stream.JsonReader
-import com.google.gson.stream.JsonToken
-import com.google.gson.stream.JsonWriter
+import kotlinx.serialization.ExperimentalSerializationApi
+import kotlinx.serialization.KSerializer
+import kotlinx.serialization.descriptors.SerialDescriptor
+import kotlinx.serialization.descriptors.buildClassSerialDescriptor
+import kotlinx.serialization.encoding.Decoder
+import kotlinx.serialization.encoding.Encoder
+import kotlinx.serialization.json.JsonArray
+import kotlinx.serialization.json.JsonDecoder
+import kotlinx.serialization.json.JsonNull
+import kotlinx.serialization.json.JsonPrimitive
+import kotlinx.serialization.json.jsonPrimitive
 
 /**
  * LNbits returns `comment` in PaymentExtra as either:
@@ -11,31 +18,29 @@ import com.google.gson.stream.JsonWriter
  *   - a JSON array    ["Thanks!"]
  *   - null
  *
- * Registered centrally in [GsonProvider] — but also applied via @JsonAdapter
- * on the field for extra safety.
+ * Mirrors the behaviour of the old Gson FlexibleStringAdapter.
  */
-class FlexibleStringAdapter : TypeAdapter<String?>() {
+object FlexibleStringSerializer : KSerializer<String?> {
 
-    override fun write(out: JsonWriter, value: String?) {
-        if (value == null) out.nullValue() else out.value(value)
+    override val descriptor: SerialDescriptor =
+        buildClassSerialDescriptor("FlexibleString")
+
+    @OptIn(ExperimentalSerializationApi::class)
+    override fun serialize(encoder: Encoder, value: String?) {
+        if (value == null) encoder.encodeNull()
+        else encoder.encodeString(value)
     }
 
-    override fun read(reader: JsonReader): String? {
-        return when (reader.peek()) {
-            JsonToken.NULL -> { reader.nextNull(); null }
-            JsonToken.BEGIN_ARRAY -> {
-                val parts = mutableListOf<String>()
-                reader.beginArray()
-                while (reader.hasNext()) {
-                    when (reader.peek()) {
-                        JsonToken.NULL -> reader.nextNull()
-                        else           -> parts.add(reader.nextString())
-                    }
-                }
-                reader.endArray()
-                parts.joinToString(", ").ifEmpty { null }
-            }
-            else -> reader.nextString()
+    override fun deserialize(decoder: Decoder): String? {
+        val jsonDecoder = decoder as JsonDecoder
+        return when (val element = jsonDecoder.decodeJsonElement()) {
+            is JsonNull -> null
+            is JsonPrimitive -> element.content                  // plain string → as-is
+            is JsonArray -> element                          // array → join elements
+                .mapNotNull { if (it is JsonNull) null else it.jsonPrimitive.content }
+                .joinToString(", ")
+                .ifEmpty { null }
+            else             -> null
         }
     }
-}
+}

app/src/main/java/com/bitcointxoko/gudariwallet/api/GsonProvider.kt

@@ -1,21 +0,0 @@
-package com.bitcointxoko.gudariwallet.api
-
-import com.google.gson.Gson
-import com.google.gson.GsonBuilder
-
-/**
- * Single source of truth for the app's Gson instance.
- *
- * All serialization/deserialization — Retrofit, SharedPreferences caches,
- * and WebSocket message parsing — must use this instance so that registered
- * type adapters (e.g. [SuccessActionAdapter]) are applied consistently
- * everywhere.
- *
- * To add a new adapter: register it here once. It will automatically apply
- * to every deserialization path in the app.
- */
-object GsonProvider {
-    val gson: Gson = GsonBuilder()
-        .registerTypeAdapter(SuccessAction::class.java, SuccessActionAdapter())
-        .create()
-}

app/src/main/java/com/bitcointxoko/gudariwallet/api/JsonProvider.kt

@@ -0,0 +1,23 @@
+package com.bitcointxoko.gudariwallet.api
+
+import kotlinx.serialization.json.Json
+
+/**
+ * Single source of truth for the app's Json instance.
+ *
+ * All serialization/deserialization — Retrofit, DataStore caches,
+ * and WebSocket message parsing — must use this instance so that
+ * configuration is applied consistently everywhere.
+ *
+ * Custom type serializers (e.g. [SuccessActionSerializer],
+ * [FlexibleStringSerializer]) are registered directly on the model
+ * classes via @Serializable(with = ...) so no explicit registration
+ * is needed here.
+ */
+object JsonProvider {
+    val json: Json = Json {
+        ignoreUnknownKeys = true   // tolerate extra fields from the API
+        isLenient = true           // accept unquoted/malformed JSON from some endpoints
+        explicitNulls = false      // omit null fields when serializing requests
+    }
+}

app/src/main/java/com/bitcointxoko/gudariwallet/api/LNbitsClient.kt

@@ -5,9 +5,10 @@ import com.bitcointxoko.gudariwallet.util.WalletConstants
 import kotlinx.coroutines.runBlocking
 import okhttp3.HttpUrl.Companion.toHttpUrl
 import okhttp3.Interceptor
+import okhttp3.MediaType.Companion.toMediaType
 import okhttp3.OkHttpClient
 import retrofit2.Retrofit
-import retrofit2.converter.gson.GsonConverterFactory
+import retrofit2.converter.kotlinx.serialization.asConverterFactory
 import java.util.concurrent.TimeUnit
 
 object LNbitsClient {
@@ -59,8 +60,11 @@ object LNbitsClient {
         return Retrofit.Builder()
             .baseUrl("https://placeholder.invalid/")  // structurally required by Retrofit;
             .client(client)
-            .addConverterFactory(GsonConverterFactory.create(GsonProvider.gson))
-            .build()
+            .addConverterFactory(
+                JsonProvider.json.asConverterFactory(
+                    "application/json; charset=UTF-8".toMediaType()
+                )
+            )            .build()
             .create(LNbitsApi::class.java)
     }
 }

app/src/main/java/com/bitcointxoko/gudariwallet/api/Models.kt

@@ -1,50 +1,66 @@
 package com.bitcointxoko.gudariwallet.api
 
 import androidx.compose.runtime.Immutable
-import com.google.gson.TypeAdapter
-import com.google.gson.annotations.JsonAdapter
-import com.google.gson.annotations.SerializedName
-import com.google.gson.stream.JsonReader
-import com.google.gson.stream.JsonToken
-import com.google.gson.stream.JsonWriter
+import kotlinx.serialization.KSerializer
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+import kotlinx.serialization.descriptors.SerialDescriptor
+import kotlinx.serialization.descriptors.buildClassSerialDescriptor
+import kotlinx.serialization.encoding.Decoder
+import kotlinx.serialization.encoding.Encoder
+import kotlinx.serialization.json.JsonDecoder
+import kotlinx.serialization.json.JsonElement
+import kotlinx.serialization.json.JsonEncoder
+import kotlinx.serialization.json.JsonNull
+import kotlinx.serialization.json.JsonObject
+import kotlinx.serialization.json.JsonPrimitive
+import kotlinx.serialization.json.jsonObject
+import kotlinx.serialization.json.jsonPrimitive
 
 // ── Wallet ────────────────────────────────────────────────────────────────────
+@Serializable
 data class WalletResponse(
-    val id: String,
-    val name: String,
-    val balance: Long       // millisatoshis
+    val id: String = "",
+    val name: String = "",
+    val balance: Long = 0L      // millisatoshis
 )
 
 // ── Create invoice ────────────────────────────────────────────────────────────
+@Serializable
 data class CreateInvoiceRequest(
     val out: Boolean,
     val amount: Long,       // satoshis
     val memo: String
 )
 
+@Serializable
 data class CreateInvoiceResponse(
-    @SerializedName("payment_hash")    val paymentHash: String,
-    @SerializedName("payment_request") val paymentRequest: String,
-    @SerializedName("expiry")          val expiry        : String?
+    @SerialName("payment_hash")    val paymentHash: String,
+    @SerialName("payment_request") val paymentRequest: String,
+    @SerialName("expiry")          val expiry: String?
 )
 
 // ── Pay invoice ───────────────────────────────────────────────────────────────
+@Serializable
 data class PayInvoiceRequest(
     val out: Boolean,
     val bolt11: String
 )
 
+@Serializable
 data class PayInvoiceResponse(
-    @SerializedName("payment_hash") val paymentHash: String,
-    @SerializedName("checking_id")  val checkingId: String
+    @SerialName("payment_hash") val paymentHash: String,
+    @SerialName("checking_id")  val checkingId: String
 )
 
 // ── Check payment ─────────────────────────────────────────────────────────────
+@Serializable
 data class PaymentStatusResponse(
     val paid: Boolean,
     val details: PaymentDetails? = null
 )
 
+@Serializable
 data class PaymentDetails(
     val amount: Long?,
     val fee: Long?,
@@ -52,82 +68,80 @@ data class PaymentDetails(
 )
 
 // ── Decode BOLT-11 ────────────────────────────────────────────────────────────
+@Serializable
 data class DecodeInvoiceRequest(
     val data: String
 )
 
+@Serializable
 data class DecodeInvoiceResponse(
-    @SerializedName("payment_hash") val paymentHash  : String? = null,
-    @SerializedName("amount_msat")  val amountMsat   : Long?   = null,
-    @SerializedName("description")  val description  : String? = null,
-    @SerializedName("payee")        val payee        : String? = null,
-    @SerializedName("route_hints")  val routeHints   : List<List<RouteHintHop>>? = null
+    @SerialName("payment_hash") val paymentHash: String?            = null,
+    @SerialName("amount_msat")  val amountMsat: Long?               = null,
+    @SerialName("description")  val description: String?            = null,
+    @SerialName("payee")        val payee: String?                  = null,
+    @SerialName("route_hints")  val routeHints: List<List<RouteHintHop>>? = null
 )
 
-
+@Serializable
 data class RouteHintHop(
-    @SerializedName("public_key")         val publicKey       : String,
-    @SerializedName("short_channel_id")   val shortChannelId  : String? = null,
-    @SerializedName("base_fee")           val baseFeeMsat     : Long    = 0,
-    @SerializedName("ppm_fee")            val ppmFee          : Long    = 0,
-    @SerializedName("cltv_expiry_delta")  val cltvExpiryDelta : Int     = 0
+    @SerialName("public_key")        val publicKey: String,
+    @SerialName("short_channel_id")  val shortChannelId: String?  = null,
+    @SerialName("base_fee")          val baseFeeMsat: Long        = 0,
+    @SerialName("ppm_fee")           val ppmFee: Long             = 0,
+    @SerialName("cltv_expiry_delta") val cltvExpiryDelta: Int     = 0
 )
 
 // ── LNURL scan ────────────────────────────────────────────────────────────────
+@Serializable
 data class LnurlScanResponse(
     val tag: String?,
-    // ── payRequest fields ────────────────────────────────────────────────────
-    val callback: String?                = null,
-    @SerializedName("minSendable")    val minSendable: Long?    = null,
-    @SerializedName("maxSendable")    val maxSendable: Long?    = null,
-    val metadata: String?                = null,
-    @SerializedName("commentAllowed") val commentAllowed: Int?  = null,
-    @SerializedName("allowsNostr")    val allowsNostr: Boolean? = null,
-    @SerializedName("nostrPubkey")    val nostrPubkey: String?  = null,
-    val bolt11: String?                  = null,
-    @SerializedName("amount_msat")    val amountMsat: Long?     = null,
-    val disposable: Boolean?             = null,  // LUD-06: null means treat as true (do not cache)
-    // ── withdrawRequest fields ───────────────────────────────────────────────
-    val k1               : String?  = null,
-    @SerializedName("defaultDescription")
-    val defaultDescription: String? = null,
-    @SerializedName("minWithdrawable")
-    val minWithdrawable  : Long?    = null,
-    @SerializedName("maxWithdrawable")
-    val maxWithdrawable  : Long?    = null,
-    @SerializedName("balanceCheck")
-    val balanceCheck     : String?  = null,
-    @SerializedName("currentBalance")
-    val currentBalance   : Long?    = null,
-    // ── Error fields ─────────────────────────────────────────────────────────
-    val status         : String?  = null,   // "OK" or "ERROR"
-    val reason         : String?  = null    // error message when status == "ERROR"
+    // ── payRequest fields ─────────────────────────────────────────────────────
+    val callback: String?                       = null,
+    @SerialName("minSendable")    val minSendable: Long?           = null,
+    @SerialName("maxSendable")    val maxSendable: Long?           = null,
+    val metadata: String?                       = null,
+    @SerialName("commentAllowed") val commentAllowed: Int?         = null,
+    @SerialName("allowsNostr")    val allowsNostr: Boolean?        = null,
+    @SerialName("nostrPubkey")    val nostrPubkey: String?         = null,
+    val bolt11: String?                         = null,
+    @SerialName("amount_msat")    val amountMsat: Long?            = null,
+    val disposable: Boolean?                    = null,  // LUD-06: null means treat as true (do not cache)
+    // ── withdrawRequest fields ────────────────────────────────────────────────
+    val k1: String?                             = null,
+    @SerialName("defaultDescription") val defaultDescription: String? = null,
+    @SerialName("minWithdrawable")    val minWithdrawable: Long?   = null,
+    @SerialName("maxWithdrawable")    val maxWithdrawable: Long?   = null,
+    @SerialName("balanceCheck")       val balanceCheck: String?    = null,
+    @SerialName("currentBalance")     val currentBalance: Long?    = null,
+    // ── Error fields ──────────────────────────────────────────────────────────
+    val status: String?                         = null,  // "OK" or "ERROR"
+    val reason: String?                         = null   // error message when status == "ERROR"
 )
 
 // ── LNURL-pay callback response (LUD-06) ─────────────────────────────────────
+@Serializable
 data class LnurlCallbackResponse(
-    val pr            : String,           // BOLT-11 invoice to pay
-    val routes        : List<Any>?  = null,
-    @SerializedName("successAction")
-    val successAction : SuccessAction? = null,
-    // Error fields (server may return status=ERROR instead of pr)
-    val status        : String?     = null,
-    val reason        : String?     = null
+    val pr: String,
+    val routes: List<JsonElement>? = null,
+    @SerialName("successAction") val successAction: SuccessAction? = null,
+    val status: String? = null,
+    val reason: String? = null
 )
 
-
 // ── LNURL pay ─────────────────────────────────────────────────────────────────
+@Serializable
 data class LnurlPayRes(
     val tag: String?,
     val callback: String?,
-    @SerializedName("minSendable")    val minSendable: Long?,
-    @SerializedName("maxSendable")    val maxSendable: Long?,
+    @SerialName("minSendable")    val minSendable: Long?,
+    @SerialName("maxSendable")    val maxSendable: Long?,
     val metadata: String?,
-    @SerializedName("commentAllowed") val commentAllowed: Int?,
-    @SerializedName("allowsNostr")    val allowsNostr: Boolean? = null,
-    @SerializedName("nostrPubkey")    val nostrPubkey: String?  = null
+    @SerialName("commentAllowed") val commentAllowed: Int?,
+    @SerialName("allowsNostr")    val allowsNostr: Boolean? = null,
+    @SerialName("nostrPubkey")    val nostrPubkey: String?  = null
 )
 
+@Serializable
 data class PayLnurlRequest(
     val res: LnurlPayRes,
     val lnurl: String,
@@ -135,45 +149,48 @@ data class PayLnurlRequest(
     val comment: String? = null
 )
 
+@Serializable
 data class PayLnurlResponse(
-    @SerializedName("payment_hash") val paymentHash: String,
-    @SerializedName("checking_id")  val checkingId: String
+    @SerialName("payment_hash") val paymentHash: String,
+    @SerialName("checking_id")  val checkingId: String
 )
 
+@Serializable
 data class WithdrawCallbackResponse(
-    val status : String,
-    val reason : String? = null
+    val status: String,
+    val reason: String? = null
 )
 
 // ── LNURLp pay link (lightning address) ──────────────────────────────────────
+@Serializable
 data class LnurlpLink(
-    val id          : String,
-    val wallet      : String,
-    val username    : String?,      // the part before the @ in the lightning address
-    val description : String?,
-    val min         : Long,
-    val max         : Long
+    val id: String,
+    val wallet: String,
+    val username: String?,      // the part before the @ in the lightning address
+    val description: String?,
+    @Serializable(with = LongAsDoubleSerializer::class) val min: Long,
+    @Serializable(with = LongAsDoubleSerializer::class) val max: Long
 )
 
-
 // ── Payment history ───────────────────────────────────────────────────────────
 @Immutable
+@Serializable
 data class PaymentRecord(
-    @SerializedName("payment_hash") val paymentHash: String,
-    @SerializedName("checking_id")  val checkingId: String,
-    @SerializedName("amount")       val amountMsat: Long,
-    @SerializedName("fee")          val feeMsat: Long,
-    @SerializedName("memo")         val memo: String?,
-    @SerializedName("time")         val time: String,
-    @SerializedName("status")       val status: String,
-    @SerializedName("bolt11")       val bolt11: String?,
-    @SerializedName("pending")      val pending: Boolean,
-    @SerializedName("preimage")     val preimage: String?,
-    @SerializedName("extra")        val extra: PaymentExtra?,
+    @SerialName("payment_hash") val paymentHash: String = "",
+    @SerialName("checking_id")  val checkingId: String  = "",
+    @SerialName("amount")       val amountMsat: Long     = 0L,
+    @SerialName("fee")          val feeMsat: Long        = 0L,
+    @SerialName("memo")         val memo: String?        = null,
+    @SerialName("time")         val time: String         = "",
+    @SerialName("status")       val status: String       = "",
+    @SerialName("bolt11")       val bolt11: String?      = null,
+    @SerialName("pending")      val pending: Boolean     = false,
+    @SerialName("preimage")     val preimage: String?    = null,
+    @SerialName("extra")        val extra: PaymentExtra? = null,
     // Not from the API — populated only when loaded from Room via toDomain()
     val createdAt: Long? = null,
-    val pubkey: String? = null,
-    val alias:  String? = null
+    val pubkey: String?  = null,
+    val alias: String?   = null
 ) {
     val amountSat: Long     get() = kotlin.math.abs(amountMsat) / 1000L
     val feeSat: Long        get() = kotlin.math.abs(feeMsat)    / 1000L
@@ -181,13 +198,13 @@ data class PaymentRecord(
 
     companion object {
         fun fromPayment(
-            paymentHash : String,
-            amountSats  : Long,
-            feeSats     : Long?,
-            bolt11      : String?,
-            memo        : String?,
-            pubkey      : String?,
-            alias       : String?,
+            paymentHash: String,
+            amountSats: Long,
+            feeSats: Long?,
+            bolt11: String?,
+            memo: String?,
+            pubkey: String?,
+            alias: String?,
         ): PaymentRecord = PaymentRecord(
             paymentHash = paymentHash,
             checkingId  = paymentHash,
@@ -207,23 +224,25 @@ data class PaymentRecord(
 }
 
 @Immutable
-
+@Serializable
 data class PaymentExtra(
-    @SerializedName("tag")            val tag: String?,
-    @JsonAdapter(FlexibleStringAdapter::class)
-    val comment: String?,
-    @SerializedName("success_action") val successAction: SuccessAction?,
-    @SerializedName("wallet_id")      val walletId: String?,
-    @SerializedName("destination")    val destination: String?,
-    @SerializedName("expires_at")     val expiresAt: String?
+    @SerialName("tag")            val tag: String?            = null,
+    @Serializable(with = FlexibleStringSerializer::class)
+    val comment: String?        = null,
+    @SerialName("success_action") @Serializable(with = SuccessActionSerializer::class)
+    val successAction: SuccessAction? = null,
+    @SerialName("wallet_id")      val walletId: String?       = null,
+    @SerialName("destination")    val destination: String?    = null,
+    @SerialName("expires_at")     val expiresAt: String?      = null
 )
 
 @Immutable
+@Serializable(with = SuccessActionSerializer::class)
 data class SuccessAction(
-    @SerializedName("tag")         val tag: String?,
-    @SerializedName("message")     val message: String?,
-    @SerializedName("url")         val url: String?,
-    @SerializedName("description") val description: String?
+    @SerialName("tag")         val tag: String?,
+    @SerialName("message")     val message: String?,
+    @SerialName("url")         val url: String?,
+    @SerialName("description") val description: String?
 )
 
 /**
@@ -232,99 +251,101 @@ data class SuccessAction(
  *   - a plain string "Thanks!"
  *   - null
  *
- * Gson's default deserialiser throws IllegalStateException when it sees a
- * string where it expects {. This adapter handles all three cases.
+ * kotlinx.serialization's default deserialiser throws when it sees a
+ * string where it expects {. This serializer handles all three cases.
  *
- * Registered centrally in [GsonProvider] — applies to all deserialization
- * paths automatically.
+ * Applied via @Serializable(with = SuccessActionSerializer::class) on
+ * the SuccessAction class and on PaymentExtra.successAction.
  */
-class SuccessActionAdapter : TypeAdapter<SuccessAction?>() {
+object SuccessActionSerializer : KSerializer<SuccessAction?> {
 
-    override fun write(out: JsonWriter, value: SuccessAction?) {
-        if (value == null) { out.nullValue(); return }
-        out.beginObject()
-        out.name("tag");         out.value(value.tag)
-        out.name("message");     out.value(value.message)
-        out.name("url");         out.value(value.url)
-        out.name("description"); out.value(value.description)
-        out.endObject()
+    override val descriptor: SerialDescriptor =
+        buildClassSerialDescriptor("SuccessAction")
+
+    override fun serialize(encoder: Encoder, value: SuccessAction?) {
+        val jsonEncoder = encoder as JsonEncoder
+        if (value == null) {
+            jsonEncoder.encodeJsonElement(JsonNull)
+        } else {
+            jsonEncoder.encodeJsonElement(
+                JsonObject(
+                    mapOf(
+                        "tag"         to JsonPrimitive(value.tag),
+                        "message"     to JsonPrimitive(value.message),
+                        "url"         to JsonPrimitive(value.url),
+                        "description" to JsonPrimitive(value.description)
+                    )
+                )
+            )
+        }
     }
 
-    override fun read(reader: JsonReader): SuccessAction? {
-        return when (reader.peek()) {
-            JsonToken.NULL -> { reader.nextNull(); null }
-
-            // Plain string — treat as a message-type success action
-            JsonToken.STRING -> {
-                val text = reader.nextString()
+    override fun deserialize(decoder: Decoder): SuccessAction? {
+        val jsonDecoder = decoder as JsonDecoder
+        return when (val element = jsonDecoder.decodeJsonElement()) {
+            is JsonNull      -> null
+            is JsonPrimitive -> {
+                // Plain string — treat as a message-type success action
+                val text = element.jsonPrimitive.content
                 if (text.isBlank()) null
                 else SuccessAction(tag = "message", message = text, url = null, description = null)
             }
-
-            // Normal object
-            JsonToken.BEGIN_OBJECT -> {
-                reader.beginObject()
-                var tag: String? = null
-                var message: String? = null
-                var url: String? = null
-                var description: String? = null
-                while (reader.hasNext()) {
-                    when (reader.nextName()) {
-                        "tag"         -> tag         = reader.nextString()
-                        "message"     -> message     = reader.nextString()
-                        "url"         -> url         = reader.nextString()
-                        "description" -> description = reader.nextString()
-                        else          -> reader.skipValue()
-                    }
-                }
-                reader.endObject()
-                SuccessAction(tag = tag, message = message, url = url, description = description)
+            is JsonObject    -> {
+                SuccessAction(
+                    tag         = element.jsonObject["tag"]?.jsonPrimitive?.content,
+                    message     = element.jsonObject["message"]?.jsonPrimitive?.content,
+                    url         = element.jsonObject["url"]?.jsonPrimitive?.content,
+                    description = element.jsonObject["description"]?.jsonPrimitive?.content
+                )
             }
-
-            else -> { reader.skipValue(); null }
+            else             -> null
         }
     }
 }
+
 data class PaymentDetailResponse(
     val paid: Boolean,
     val details: PaymentRecord?
 )
 
 // ── WebSocket payment message ─────────────────────────────────────────────────
+@Serializable
 data class WsPaymentMessage(
-    @SerializedName("wallet_balance") val walletBalance: Long?,
+    @SerialName("wallet_balance") val walletBalance: Long?,
     val payment: WsPayment?
 )
 
+@Serializable
 data class WsPayment(
-    @SerializedName("payment_hash") val paymentHash: String,
-    @SerializedName("checking_id")  val checkingId: String,
-    @SerializedName("amount")       val amount: Long,
-    @SerializedName("fee")          val fee: Long,
-    @SerializedName("memo")         val memo: String?,
-    @SerializedName("time")         val time: String,
-    @SerializedName("status")       val status: String,
-    @SerializedName("bolt11")       val bolt11: String?,
-    @SerializedName("pending")      val pending: Boolean,
-    @SerializedName("preimage")     val preimage: String?,
-    @SerializedName("extra")        val extra: PaymentExtra?
+    @SerialName("payment_hash") val paymentHash: String,
+    @SerialName("checking_id")  val checkingId: String,
+    @SerialName("amount")       val amount: Long,
+    @SerialName("fee")          val fee: Long,
+    @SerialName("memo")         val memo: String?,
+    @SerialName("time")         val time: String,
+    @SerialName("status")       val status: String,
+    @SerialName("bolt11")       val bolt11: String?,
+    @SerialName("pending")      val pending: Boolean,
+    @SerialName("preimage")     val preimage: String?,
+    @SerialName("extra")        val extra: PaymentExtra?
 )
 
-
-// ── Fiat rate ────────────────────────────────────────────────────────────────
+// ── Fiat rate ─────────────────────────────────────────────────────────────────
+@Serializable
 data class FiatRateResponse(
     val rate: Double,   // sat to fiat rate
-    val price : Double  // BTC price in the requested fiat currency
+    val price: Double   // BTC price in the requested fiat currency
 )
 
-// ── History sync ─────────────────────────────────────────────────────────────
+// ── History sync ──────────────────────────────────────────────────────────────
+@Serializable
 data class PaginatedPaymentsResponse(
-    @SerializedName("data")  val data:  List<PaymentRecord>,
-    @SerializedName("total") val total: Int
+    @SerialName("data")  val data: List<PaymentRecord>,
+    @SerialName("total") val total: Int
 )
 
 // ── NWC Provider models ───────────────────────────────────────────────────────
-
+@Serializable
 data class NwcKey(
     val pubkey: String,
     val wallet: String,
@@ -335,6 +356,7 @@ data class NwcKey(
     val last_used: Long
 )
 
+@Serializable
 data class NwcBudget(
     val id: Int,
     val pubkey: String,
@@ -344,22 +366,41 @@ data class NwcBudget(
     val used_budget_msats: Long = 0
 )
 
-/** Response for GET /nwc and GET /nwc/{pubkey} */
+@Serializable
 data class NwcGetResponse(
     val data: NwcKey,
     val budgets: List<NwcBudget>
 )
 
+@Serializable
 data class NwcNewBudget(
     val budget_msats: Long,
     val refresh_window: Int,        // seconds
-    val created_at    : Long = System.currentTimeMillis() / 1000L
+    val created_at: Long = System.currentTimeMillis() / 1000L
 )
 
-/** Request body for PUT /nwc/{pubkey} */
+@Serializable
 data class NwcRegistrationRequest(
     val permissions: List<String>,
     val description: String,
-    val expires_at: Long,          // unix timestamp; 0 = no expiry
+    val expires_at: Long,           // unix timestamp; 0 = no expiry
     val budgets: List<NwcNewBudget> = emptyList()
 )
+
+/**
+ * Deserializes a JSON number that may arrive as either an integer (1)
+ * or a float (1.0) into a Long, truncating any fractional part.
+ */
+object LongAsDoubleSerializer : KSerializer<Long> {
+    override val descriptor = buildClassSerialDescriptor("LongAsDouble")
+
+    override fun serialize(encoder: Encoder, value: Long) = encoder.encodeLong(value)
+
+    override fun deserialize(decoder: Decoder): Long {
+        val jsonDecoder = decoder as JsonDecoder
+        return when (val element = jsonDecoder.decodeJsonElement()) {
+            is JsonPrimitive -> element.content.toDouble().toLong()
+            else -> 0L
+        }
+    }
+}

app/src/main/java/com/bitcointxoko/gudariwallet/api/NodeAliasApi.kt

@@ -1,10 +1,12 @@
 package com.bitcointxoko.gudariwallet.api
 
+import kotlinx.serialization.Serializable
 import retrofit2.http.GET
 import retrofit2.http.Path
 
 // ── mempool.space ─────────────────────────────────────────────────────────────
 
+@Serializable
 data class MempoolNodeResponse(
     val alias: String?,
     val public_key: String?
@@ -17,6 +19,7 @@ interface MempoolApi {
 
 // ── 1ml.com ───────────────────────────────────────────────────────────────────
 
+@Serializable
 data class OneMlNodeResponse(
     val alias: String?,
     val pub_key: String?

app/src/main/java/com/bitcointxoko/gudariwallet/api/NodeAliasClient.kt.kt

@@ -1,8 +1,9 @@
 package com.bitcointxoko.gudariwallet.api
 
+import okhttp3.MediaType.Companion.toMediaType
 import okhttp3.OkHttpClient
 import retrofit2.Retrofit
-import retrofit2.converter.gson.GsonConverterFactory
+import retrofit2.converter.kotlinx.serialization.asConverterFactory
 import java.util.concurrent.TimeUnit
 
 /**
@@ -17,17 +18,20 @@ class NodeAliasClient {
         .readTimeout(5, TimeUnit.SECONDS)
         .build()
 
+    private val converter = JsonProvider.json
+        .asConverterFactory("application/json; charset=UTF-8".toMediaType())
+
     private val mempoolApi: MempoolApi = Retrofit.Builder()
         .baseUrl("https://mempool.space/")
         .client(client)
-        .addConverterFactory(GsonConverterFactory.create())
+        .addConverterFactory(converter)
         .build()
         .create(MempoolApi::class.java)
 
     private val oneMlApi: OneMlApi = Retrofit.Builder()
         .baseUrl("https://1ml.com/")
         .client(client)
-        .addConverterFactory(GsonConverterFactory.create())
+        .addConverterFactory(converter)
         .build()
         .create(OneMlApi::class.java)
 

app/src/main/java/com/bitcointxoko/gudariwallet/data/FiatDataStore.kt

@@ -10,10 +10,11 @@ import androidx.datastore.preferences.core.floatPreferencesKey
 import androidx.datastore.preferences.core.longPreferencesKey
 import androidx.datastore.preferences.core.stringPreferencesKey
 import androidx.datastore.preferences.preferencesDataStore
-import com.google.gson.Gson
-import com.google.gson.reflect.TypeToken
+import com.bitcointxoko.gudariwallet.api.JsonProvider
 import kotlinx.coroutines.flow.catch
 import kotlinx.coroutines.flow.first
+import kotlinx.serialization.builtins.ListSerializer
+import kotlinx.serialization.builtins.serializer
 import java.io.IOException
 
 private const val TAG = "FiatDataStore"
@@ -27,13 +28,13 @@ private val Context.fiatDataStore: DataStore<Preferences> by preferencesDataStor
 class FiatDataStore(context: Context) {
 
     private val dataStore = context.applicationContext.fiatDataStore
-    private val gson = Gson()
+    private val json = JsonProvider.json
 
     // ── Key factories ─────────────────────────────────────────────────────────
 
-    private fun rateKey(currency: String)        = floatPreferencesKey("fiat_rate_$currency")
+    private fun rateKey(currency: String)          = floatPreferencesKey("fiat_rate_$currency")
     private fun rateFetchedAtKey(currency: String) = longPreferencesKey("fiat_rate_fetched_at_$currency")
-    private val currenciesKey                    = stringPreferencesKey("fiat_currencies_json")
+    private val currenciesKey                      = stringPreferencesKey("fiat_currencies_json")
 
     // ── Rate ──────────────────────────────────────────────────────────────────
 
@@ -87,10 +88,9 @@ class FiatDataStore(context: Context) {
                 } else throw e
             }
             .first()
-        val json = prefs[currenciesKey] ?: return null
+        val jsonString = prefs[currenciesKey] ?: return null
         return runCatching {
-            val type = object : TypeToken<List<String>>() {}.type
-            val list: List<String> = gson.fromJson(json, type)
+            val list = json.decodeFromString(ListSerializer(String.serializer()), jsonString)
             Timber.d("FIAT [CURRENCIES] DataStore hit (${list.size} currencies)")
             list
         }.getOrElse { e ->
@@ -106,7 +106,7 @@ class FiatDataStore(context: Context) {
         if (currencies.isEmpty()) return
         runCatching {
             dataStore.edit { prefs ->
-                prefs[currenciesKey] = gson.toJson(currencies)
+                prefs[currenciesKey] = json.encodeToString(ListSerializer(String.serializer()), currencies)
             }
         }.onFailure { e ->
             Timber.w("FIAT [CURRENCIES] persist failed — ${e.message}")

app/src/main/java/com/bitcointxoko/gudariwallet/data/LnurlCacheRepository.kt

@@ -2,7 +2,7 @@ package com.bitcointxoko.gudariwallet.data
 
 import android.content.Context
 import timber.log.Timber
-import com.bitcointxoko.gudariwallet.api.GsonProvider
+import com.bitcointxoko.gudariwallet.api.JsonProvider
 import com.bitcointxoko.gudariwallet.api.LnurlScanResponse
 import com.bitcointxoko.gudariwallet.data.db.AppDatabase
 import com.bitcointxoko.gudariwallet.data.db.LnurlCacheEntity
@@ -13,7 +13,7 @@ private const val TAG = "LnurlCacheRepository"
 class LnurlCacheRepository(context: Context) {
 
     private val dao = AppDatabase.getInstance(context).lnurlCacheDao()
-    private val gson = GsonProvider.gson
+    private val json = JsonProvider.json
 
     // Fast in-memory path — avoids a DB round-trip for keys already loaded
     // this session. Mirrors the pattern used in PaymentCacheRepository.
@@ -62,13 +62,13 @@ class LnurlCacheRepository(context: Context) {
      */
     suspend fun put(key: String, response: LnurlScanResponse) {
         val disposable = response.disposable
-        if ( disposable == true) {
+        if (disposable == true) {
             Timber.d("LNURL [SKIP CACHE ] $key — disposable=$disposable, not caching")
             return
         }
         val entity = LnurlCacheEntity(
             key          = key,
-            responseJson = gson.toJson(response),
+            responseJson = json.encodeToString(LnurlScanResponse.serializer(), response),
             savedAt      = System.currentTimeMillis()
         )
         runCatching {
@@ -104,7 +104,7 @@ class LnurlCacheRepository(context: Context) {
         runCatching { dao.deleteByKey(key) }
     }
 
-    private fun deserialise(json: String): LnurlScanResponse? =
-        runCatching { gson.fromJson(json, LnurlScanResponse::class.java) }
+    private fun deserialise(jsonString: String): LnurlScanResponse? =
+        runCatching { json.decodeFromString(LnurlScanResponse.serializer(), jsonString) }
             .getOrNull()
 }

app/src/main/java/com/bitcointxoko/gudariwallet/data/db/PaymentConverters.kt

@@ -1,19 +1,19 @@
 package com.bitcointxoko.gudariwallet.data.db
 
 import androidx.room.TypeConverter
+import com.bitcointxoko.gudariwallet.api.JsonProvider
 import com.bitcointxoko.gudariwallet.api.PaymentExtra
-import com.bitcointxoko.gudariwallet.api.GsonProvider
 
 object PaymentConverters {
-    private val gson = GsonProvider.gson
+    private val json = JsonProvider.json
 
     @TypeConverter
     @JvmStatic
     fun fromExtra(extra: PaymentExtra?): String? =
-        extra?.let { gson.toJson(it) }
+        extra?.let { json.encodeToString(PaymentExtra.serializer(), it) }
 
     @TypeConverter
     @JvmStatic
-    fun toExtra(json: String?): PaymentExtra? =
-        json?.let { gson.fromJson(it, PaymentExtra::class.java) }
+    fun toExtra(string: String?): PaymentExtra? =
+        string?.let { json.decodeFromString(PaymentExtra.serializer(), it) }
 }

app/src/main/java/com/bitcointxoko/gudariwallet/data/db/PaymentRecordMapper.kt

@@ -1,12 +1,12 @@
 package com.bitcointxoko.gudariwallet.data.db
 
 import timber.log.Timber
-import com.bitcointxoko.gudariwallet.api.GsonProvider.gson
+import com.bitcointxoko.gudariwallet.api.JsonProvider
+import com.bitcointxoko.gudariwallet.api.PaymentExtra
 import com.bitcointxoko.gudariwallet.api.PaymentRecord
-import com.bitcointxoko.gudariwallet.data.db.PaymentRecordEntity
 
 private const val TAG = "PaymentMappers"
-
+private val json = JsonProvider.json
 
 // ── Parse helper — runs once at write time, never again ──────────────────────
 
@@ -36,10 +36,10 @@ fun PaymentRecord.toEntity(savedAt: Long): PaymentRecordEntity =
         bolt11      = bolt11,
         pending     = pending,
         preimage    = preimage,
-        extra       = extra?.let { gson.toJson(it) },
+        extra       = extra?.let { json.encodeToString(PaymentExtra.serializer(), it) },
         savedAt     = savedAt,
-        pubkey = pubkey,
-        alias  = alias
+        pubkey      = pubkey,
+        alias       = alias
     )
 
 // ── PaymentRecordEntity → PaymentRecord ──────────────────────────────────────
@@ -57,7 +57,7 @@ fun PaymentRecordEntity.toDomain(): PaymentRecord =
         bolt11      = bolt11,
         pending     = pending,
         preimage    = preimage,
-        extra       = extra?.let { gson.fromJson(it, com.bitcointxoko.gudariwallet.api.PaymentExtra::class.java) },
-        pubkey = pubkey,
-        alias  = alias
+        extra       = extra?.let { json.decodeFromString(PaymentExtra.serializer(), it) },
+        pubkey      = pubkey,
+        alias       = alias
     )

app/src/main/java/com/bitcointxoko/gudariwallet/service/WalletNotificationService.kt

@@ -7,7 +7,7 @@ import android.content.pm.ServiceInfo
 import android.os.Build
 import android.os.IBinder
 import timber.log.Timber
-import com.bitcointxoko.gudariwallet.api.GsonProvider
+import com.bitcointxoko.gudariwallet.api.JsonProvider
 import com.bitcointxoko.gudariwallet.api.LNbitsClient
 import com.bitcointxoko.gudariwallet.api.PaymentRecord
 import com.bitcointxoko.gudariwallet.api.WsPaymentMessage
@@ -98,7 +98,7 @@ class WalletNotificationService : Service() {
     private var reconnectAttempts = 0
     private var currentBackoffMs = WalletConstants.WS_INITIAL_BACKOFF_MS
 
-    private val gson = GsonProvider.gson
+    private val json = JsonProvider.json
     // ── Lifecycle ─────────────────────────────────────────────────────────────
 
     override fun onStartCommand(intent: Intent?, flags: Int, startId: Int): Int {
@@ -193,7 +193,7 @@ class WalletNotificationService : Service() {
 
     private fun handleMessage(text: String) {
         val msg = runCatching {
-            gson.fromJson(text, WsPaymentMessage::class.java)
+            json.decodeFromString(WsPaymentMessage.serializer(), text)
         }.getOrNull() ?: return
 
         val payment = msg.payment ?: return

gradle/libs.versions.toml

@@ -1,9 +1,7 @@
 [versions]
 agp = "9.2.1"
 biometric = "1.2.0-alpha05"
-converterGson = "3.0.0"
 coreKtx = "1.10.1"
-gson = "2.14.0"
 junit = "4.13.2"
 junitVersion = "1.1.5"
 espressoCore = "3.5.1"
@@ -34,14 +32,13 @@ benchmark = "1.4.1"
 runner = "1.5.2"
 androidx-test-ext = "1.2.1"
 timber = "5.0.1"
+kotlinx-serialization = "1.8.1"
 
 [libraries]
 androidx-biometric = { module = "androidx.biometric:biometric", version.ref = "biometric" }
 androidx-compose-animation = { module = "androidx.compose.animation:animation" }
 androidx-core-ktx = { group = "androidx.core", name = "core-ktx", version.ref = "coreKtx" }
 androidx-lifecycle-viewmodel-ktx = { module = "androidx.lifecycle:lifecycle-viewmodel-ktx", version.ref = "lifecycleViewmodelKtx" }
-converter-gson = { module = "com.squareup.retrofit2:converter-gson", version.ref = "converterGson" }
-gson = { module = "com.google.code.gson:gson", version.ref = "gson" }
 junit = { group = "junit", name = "junit", version.ref = "junit" }
 androidx-junit = { group = "androidx.test.ext", name = "junit", version.ref = "junitVersion" }
 androidx-espresso-core = { group = "androidx.test.espresso", name = "espresso-core", version.ref = "espressoCore" }
@@ -83,6 +80,9 @@ androidx-benchmark-junit4 = { group = "androidx.benchmark", name = "benchmark-ju
 androidx-runner = { group = "androidx.test", name = "runner", version.ref = "runner" }
 androidx-test-ext-junit = { group = "androidx.test.ext", name = "junit", version.ref = "androidx-test-ext" }
 timber = { group = "com.jakewharton.timber", name = "timber", version.ref = "timber" }
+kotlinx-serialization-json = { module = "org.jetbrains.kotlinx:kotlinx-serialization-json", version.ref = "kotlinx-serialization" }
+converter-kotlinx-serialization = { module = "com.squareup.retrofit2:converter-kotlinx-serialization", version.ref = "retrofit" }
+
 
 [plugins]
 android-application = { id = "com.android.application", version.ref = "agp" }
@@ -93,3 +93,4 @@ protobuf = { id = "com.google.protobuf", version.ref = "protobufPlugin" }
 androidx-benchmark = { id = "androidx.benchmark", version.ref = "benchmark" }
 android-library = { id = "com.android.library", version.ref = "agp" }
 android-test         = { id = "com.android.test", version.ref = "agp" }
+kotlin-serialization = { id = "org.jetbrains.kotlin.plugin.serialization", version.ref = "kotlin" }