Tolerate lone-surrogate escapes in JSON strings

dotnet/EcencyApi.Tests/JsValTests.cs

@@ -49,6 +49,27 @@ public void NumberCoerce_MatchesJs(string input, double expected)
         else Assert.Equal(expected, actual);
     }
 
+    [Fact]
+    public void LoneSurrogates_ExtractAndSerializeLikeJs()
+    {
+        // JSON.parse accepts lone surrogate escapes (a JS string is arbitrary
+        // UTF-16); System.Text.Json throws InvalidOperationException when
+        // materializing such strings, which turned payloads the Node service
+        // handled fine into 500s. The lenient path must extract them, and
+        // Stringify must re-emit the escape like well-formed JSON.stringify.
+        var node = JsonNode.Parse("{\"app\":\"x\\ud83dy\"}")!;
+
+        var s = JsVal.AsString(node["app"]);
+        Assert.NotNull(s);
+        Assert.Equal(3, s!.Length);
+        Assert.Equal('\ud83d', s[1]);
+
+        Assert.Equal("{\"app\":\"x\\ud83dy\"}", JsJson.Stringify(node));
+
+        // ToJsString (template-literal coercion) must survive it too
+        Assert.Equal("x\ud83dy", JsVal.ToJsString(node["app"]));
+    }
+
     [Fact]
     public void ToJsString_CoercesLikeJs()
     {

dotnet/EcencyApi.Tests/fixtures/crypto-vectors.json

@@ -1470,6 +1470,11 @@
   }
  ],
  "validateCodeRaw": [
+  {
+   "tokenJson": "{\"signed_message\":{\"type\":\"code\",\"app\":\"x\\ud83dy\"},\"authors\":[\"mallory\"],\"timestamp\":1752300000,\"signatures\":[\"ab\"]}",
+   "rawMessage": "{\"signed_message\":{\"type\":\"code\",\"app\":\"x\\ud83dy\"},\"authors\":[\"mallory\"],\"timestamp\":1752300000}",
+   "digestHex": "6162f04277a85ad43b614e076d81a317ad873450ff71176ff4715ea0844b5e78"
+  },
   {
    "tokenJson": "{\"signed_message\":{\"type\":\"code\",\"app\":\"ecency.app\"},\"authors\":[\"alice\"],\"timestamp\":1751900000,\"signatures\":[\"ab\"]}",
    "rawMessage": "{\"signed_message\":{\"type\":\"code\",\"app\":\"ecency.app\"},\"authors\":[\"alice\"],\"timestamp\":1751900000}",

dotnet/EcencyApi/Handlers/AuthApi.cs

@@ -60,7 +60,7 @@ private static string JsToString(JsonNode? node)
                 // Array.prototype.toString: elements joined with ",", null -> ""
                 return string.Join(",", arr.Select(e => e == null ? "" : JsToString(e)));
             case JsonValue v:
-                if (v.TryGetValue<string>(out var s)) return s;
+                if (JsVal.TryGetStringLenient(v, out var s)) return s;
                 if (v.TryGetValue<bool>(out var b)) return b ? "true" : "false";
                 return JsJson.Stringify(v);
             default:

dotnet/EcencyApi/Handlers/HiveExplorer.cs

@@ -128,7 +128,7 @@ public static double ParseToken(JsonNode? val)
             return 0d;
         }
 
-        if (val is not JsonValue jv || !jv.TryGetValue<string>(out var s))
+        if (val is not JsonValue jv || !JsVal.TryGetStringLenient(jv, out var s))
         {
             return 0d;
         }
@@ -166,7 +166,7 @@ private static double ParseFloatJs(string s)
     // TypeError), which the outer catch rewrites to "Failed to get globalProps".
     private static double GetVestAmount(JsonNode? value)
     {
-        if (value is JsonValue jv && jv.TryGetValue<string>(out _))
+        if (value is JsonValue jv && JsVal.TryGetStringLenient(jv, out _))
         {
             return ParseToken(value);
         }
@@ -238,7 +238,7 @@ private static double JsNumber(JsonNode? node)
                         {
                             return double.NaN; // "true"/"false" don't parse
                         }
-                        if (ev.TryGetValue<string>(out var es))
+                        if (JsVal.TryGetStringLenient(ev, out var es))
                         {
                             return JsNumberString(es);
                         }
@@ -252,7 +252,7 @@ private static double JsNumber(JsonNode? node)
                 {
                     return b ? 1d : 0d;
                 }
-                if (value.TryGetValue<string>(out var str))
+                if (JsVal.TryGetStringLenient(value, out var str))
                 {
                     return JsNumberString(str);
                 }

dotnet/EcencyApi/Handlers/PrivateApi.Accounts.cs

@@ -69,7 +69,7 @@ public static string SignupClientIp(HttpContext ctx)
     private static async Task<bool> VerifyTurnstile(JsonNode? token, string ip)
     {
         var secret = Config.TurnstileSecret;
-        var tokenStr = token is JsonValue tv && tv.TryGetValue<string>(out string? ts) ? ts : null;
+        var tokenStr = token is JsonValue tv && JsVal.TryGetStringLenient(tv, out string? ts) ? ts : null;
         if (string.IsNullOrEmpty(secret) || tokenStr == null || tokenStr.Trim().Length == 0)
         {
             return false;

dotnet/EcencyApi/Handlers/PrivateApi.Chain.cs

@@ -259,7 +259,7 @@ private static string RpcErrorMessage(JsonNode? errorNode, string fallback)
 
     private static string ParseHexBalance(JsonNode? value)
     {
-        if (value is not JsonValue jsonValue || !jsonValue.TryGetValue<string>(out var text))
+        if (value is not JsonValue jsonValue || !JsVal.TryGetStringLenient(jsonValue, out var text))
         {
             throw new Exception("Invalid hexadecimal balance response");
         }
@@ -595,7 +595,7 @@ private static async Task<string> GetBlockstreamAccessToken()
         var data = resp.BodyIsJson ? resp.Json : JsonValue.Create(resp.RawText);
         var obj = data as JsonObject;
 
-        var accessToken = obj?["access_token"] is JsonValue tokenValue && tokenValue.TryGetValue<string>(out var tokenText)
+        var accessToken = obj?["access_token"] is JsonValue tokenValue && JsVal.TryGetStringLenient(tokenValue, out var tokenText)
             ? tokenText
             : null;
 
@@ -1107,7 +1107,7 @@ public static async Task ChainRpc(HttpContext ctx)
         null => "null",
         JsonObject => "[object Object]",
         JsonArray arr => string.Join(",", arr.Select(ChainJsString)),
-        JsonValue v when v.TryGetValue<string>(out var s) => s,
+        JsonValue v when JsVal.TryGetStringLenient(v, out var s) => s,
         _ => JsJson.Stringify(node),
     };
 

dotnet/EcencyApi/Handlers/PrivateApi.Core.cs

@@ -37,7 +37,7 @@ public static partial class PrivateApi
     {
         var hasCode = body.TryGetPropertyValue("code", out var codeNode);
         string? code = null;
-        if (codeNode is JsonValue codeValue && codeValue.TryGetValue<string>(out var codeStr))
+        if (codeNode is JsonValue codeValue && JsVal.TryGetStringLenient(codeValue, out var codeStr))
         {
             code = codeStr;
         }
@@ -98,7 +98,7 @@ public static partial class PrivateApi
 
             string? author = null;
             if (authors is { Count: > 0 } && authors[0] is JsonValue authorValue
-                && authorValue.TryGetValue<string>(out var authorStr))
+                && JsVal.TryGetStringLenient(authorValue, out var authorStr))
             {
                 author = authorStr;
             }
@@ -109,7 +109,7 @@ timestampNode is JsonValue timestampValue
 
             string? signature = null;
             if (signatures is { Count: > 0 } && signatures[0] is JsonValue signatureValue
-                && signatureValue.TryGetValue<string>(out var signatureStr))
+                && JsVal.TryGetStringLenient(signatureValue, out var signatureStr))
             {
                 signature = signatureStr;
             }
@@ -210,7 +210,7 @@ timestampNode is JsonValue timestampValue
             }
 
             var first = item[0]; // throws for non-indexable nodes, like JS destructuring a non-iterable
-            keys.Add(first is JsonValue v && v.TryGetValue<string>(out var key) ? key : null);
+            keys.Add(first is JsonValue v && JsVal.TryGetStringLenient(v, out var key) ? key : null);
         }
 
         return keys;

dotnet/EcencyApi/Handlers/PrivateApi.Feeds.cs

@@ -297,7 +297,7 @@ private static string FeedsJsToString(JsonNode? node)
                     JsonObject => "[object Object]",
                     _ => FeedsJsToString(e),
                 }));
-            case JsonValue v when v.TryGetValue<string>(out var s):
+            case JsonValue v when JsVal.TryGetStringLenient(v, out var s):
                 return s;
             case JsonValue v when v.TryGetValue<bool>(out var b):
                 return b ? "true" : "false";

dotnet/EcencyApi/Handlers/PrivateApi.Misc.cs

@@ -27,7 +27,7 @@ private static string MiscJsString(JsonNode? node)
         }
         if (node is JsonValue v)
         {
-            if (v.TryGetValue<string>(out var s))
+            if (JsVal.TryGetStringLenient(v, out var s))
             {
                 return s;
             }

dotnet/EcencyApi/Handlers/PrivateApi.Payments.cs

@@ -148,7 +148,7 @@ public static async Task StripeCreateIntent(HttpContext ctx)
         // Reject a malformed value at this boundary before forwarding (typeof guard first:
         // a non-string must never be coerced by the regex test and forwarded).
         var hostingTargetPresent = body.TryGetPropertyValue("hosting_target", out var hostingTargetNode);
-        var hostingTarget = hostingTargetNode is JsonValue htv && htv.TryGetValue<string>(out var hts)
+        var hostingTarget = hostingTargetNode is JsonValue htv && JsVal.TryGetStringLenient(htv, out var hts)
             ? hts
             : null;
         if (hostingTargetPresent && (hostingTarget == null || !PaymentsHiveNameRegex.IsMatch(hostingTarget)))
@@ -160,7 +160,7 @@ public static async Task StripeCreateIntent(HttpContext ctx)
         // lowercase, so normalize typed input (trim + lowercase) before validating so a
         // recipient like "Alice" is accepted as "alice", and forward the canonical form.
         var giftRecipientPresent = body.TryGetPropertyValue("gift_recipient", out var giftRecipientNode);
-        var giftRecipient = giftRecipientNode is JsonValue grv && grv.TryGetValue<string>(out var grs)
+        var giftRecipient = giftRecipientNode is JsonValue grv && JsVal.TryGetStringLenient(grv, out var grs)
             ? grs.Trim().ToLowerInvariant()
             : null;
         if (giftRecipientPresent && (giftRecipient == null || !PaymentsHiveNameRegex.IsMatch(giftRecipient)))
@@ -169,7 +169,7 @@ public static async Task StripeCreateIntent(HttpContext ctx)
             return;
         }
         var giftMessagePresent = body.TryGetPropertyValue("gift_message", out var giftMessageNode);
-        var giftMessage = giftMessageNode is JsonValue gmv && gmv.TryGetValue<string>(out var gms)
+        var giftMessage = giftMessageNode is JsonValue gmv && JsVal.TryGetStringLenient(gmv, out var gms)
             ? gms
             : null;
         if (giftMessagePresent && (giftMessage == null || giftMessage.Length > 200))
@@ -392,7 +392,7 @@ private static string PaymentsSignupClientIp(HttpContext ctx)
     private static async Task<bool> PaymentsVerifyTurnstile(JsonNode? token, string ip)
     {
         var secret = Config.TurnstileSecret;
-        var tokenStr = token is JsonValue tv && tv.TryGetValue<string>(out var ts) ? ts : null;
+        var tokenStr = token is JsonValue tv && JsVal.TryGetStringLenient(tv, out var ts) ? ts : null;
         if (string.IsNullOrEmpty(secret) || tokenStr == null || tokenStr.Trim().Length == 0)
         {
             return false;
@@ -474,7 +474,7 @@ private static string PaymentsJsToString(JsonNode? node)
             case JsonObject:
                 return "[object Object]";
             case JsonValue value:
-                if (value.TryGetValue<string>(out var s))
+                if (JsVal.TryGetStringLenient(value, out var s))
                 {
                     return s;
                 }

dotnet/EcencyApi/Handlers/PrivateApi.UserData1.cs

@@ -405,7 +405,7 @@ public static string Template(JsonNode? node)
                 // Array.prototype.toString: elements joined by ",", holes/null -> ""
                 return string.Join(",", arr.Select(item => item == null ? "" : Template(item)));
             default:
-                if (node is JsonValue jv && jv.TryGetValue<string>(out var s))
+                if (node is JsonValue jv && JsVal.TryGetStringLenient(jv, out var s))
                 {
                     return s;
                 }

dotnet/EcencyApi/Handlers/PrivateApi.UserData2.cs

@@ -328,7 +328,7 @@ private static string JsString(JsonNode? node)
                 // Array.prototype.toString: join(","), null/undefined elements -> ""
                 return string.Join(",", arr.Select(el => el == null ? "" : JsString(el)));
             case JsonValue v:
-                if (v.TryGetValue<string>(out var s)) return s;
+                if (JsVal.TryGetStringLenient(v, out var s)) return s;
                 if (v.TryGetValue<bool>(out var b)) return b ? "true" : "false";
                 // numbers: String(n) == JSON.stringify(n) for finite doubles
                 return JsJson.Stringify(node);

dotnet/EcencyApi/Handlers/SearchApi.cs

@@ -54,7 +54,7 @@ private static string JsToString(JsonNode? node)
                 // Array.prototype.toString: elements joined with ",", null -> ""
                 return string.Join(",", arr.Select(e => e == null ? "" : JsToString(e)));
             case JsonValue v:
-                if (v.TryGetValue<string>(out var s)) return s;
+                if (JsVal.TryGetStringLenient(v, out var s)) return s;
                 if (v.TryGetValue<bool>(out var b)) return b ? "true" : "false";
                 return JsJson.Stringify(v);
             default:

dotnet/EcencyApi/Infrastructure/ApiClient.cs

@@ -43,7 +43,7 @@ public ApiAuthException() : base("Api auth couldn't be create!") { }
             {
                 headers[kv.Key] = kv.Value switch
                 {
-                    JsonValue v when v.TryGetValue<string>(out var s) => s,
+                    JsonValue v when JsVal.TryGetStringLenient(v, out var s) => s,
                     null => "null",
                     _ => kv.Value.ToJsonString(),
                 };

dotnet/EcencyApi/Infrastructure/HttpContextExtensions.cs

@@ -92,7 +92,7 @@ public static async Task SendJson(this HttpContext ctx, int status, JsonNode? no
 
     /// <summary>Convenience: string body field (undefined -> null).</summary>
     public static string? Str(this JsonObject body, string key) =>
-        body.TryGetPropertyValue(key, out var v) && v is JsonValue val && val.TryGetValue<string>(out var s)
+        body.TryGetPropertyValue(key, out var v) && v is JsonValue val && JsVal.TryGetStringLenient(val, out var s)
             ? s
             : null;
 

dotnet/EcencyApi/Infrastructure/JsJson.cs

@@ -63,7 +63,7 @@ private static void WriteValue(StringBuilder sb, JsonNode? node)
 
     private static void WritePrimitive(StringBuilder sb, JsonValue value)
     {
-        if (value.TryGetValue<string>(out var s))
+        if (JsVal.TryGetStringLenient(value, out var s))
         {
             WriteString(sb, s);
             return;
@@ -260,7 +260,7 @@ public static bool IsTruthy(JsonNode? node)
             case JsonArray:
                 return true;
             case JsonValue v:
-                if (v.TryGetValue<string>(out var s)) return s.Length > 0;
+                if (JsVal.TryGetStringLenient(v, out var s)) return s.Length > 0;
                 if (v.TryGetValue<bool>(out var b)) return b;
                 // Parsed values are element-backed; programmatically built ones
                 // are CLR-backed and would throw on GetValue<JsonElement>().

dotnet/EcencyApi/Infrastructure/JsVal.cs

@@ -19,7 +19,7 @@ public static class JsVal
     public static bool IsString(JsonNode? n) =>
         n is JsonValue v && v.TryGetValue<JsonElement>(out var e)
             ? e.ValueKind == JsonValueKind.String
-            : n is JsonValue v2 && v2.TryGetValue<string>(out _);
+            : n is JsonValue v2 && JsVal.TryGetStringLenient(v2, out _);
 
     public static bool IsNumber(JsonNode? n)
     {
@@ -41,12 +41,77 @@ public static bool IsBool(JsonNode? n)
 
     // ---- accessors -------------------------------------------------------
 
+    /// <summary>
+    /// String extraction tolerant of lone-surrogate \u escapes. JavaScript's
+    /// JSON.parse accepts them (JS strings are arbitrary UTF-16), but
+    /// System.Text.Json throws InvalidOperationException when materializing
+    /// such strings — which turned payloads the Node service handled fine into
+    /// 500s. Falls back to manually unescaping the raw JSON text with JS
+    /// semantics (\uXXXX decodes to the code unit, paired or not).
+    /// </summary>
+    public static bool TryGetStringLenient(JsonValue v, out string value)
+    {
+        try
+        {
+            if (v.TryGetValue<string>(out value!))
+            {
+                return true;
+            }
+        }
+        catch (InvalidOperationException)
+        {
+            // incomplete surrogate pair in the JSON text; fall through
+        }
+
+        if (v.TryGetValue<JsonElement>(out var el) && el.ValueKind == JsonValueKind.String)
+        {
+            value = UnescapeJsonStringLenient(el.GetRawText());
+            return true;
+        }
+
+        value = null!;
+        return false;
+    }
+
+    /// <summary>Unescape a raw JSON string literal (including quotes) with JS semantics.</summary>
+    internal static string UnescapeJsonStringLenient(string raw)
+    {
+        var sb = new StringBuilder(raw.Length);
+        for (var i = 1; i < raw.Length - 1; i++)
+        {
+            var c = raw[i];
+            if (c != '\\')
+            {
+                sb.Append(c);
+                continue;
+            }
+            i++;
+            switch (raw[i])
+            {
+                case '"': sb.Append('"'); break;
+                case '\\': sb.Append('\\'); break;
+                case '/': sb.Append('/'); break;
+                case 'b': sb.Append('\b'); break;
+                case 'f': sb.Append('\f'); break;
+                case 'n': sb.Append('\n'); break;
+                case 'r': sb.Append('\r'); break;
+                case 't': sb.Append('\t'); break;
+                case 'u':
+                    sb.Append((char)ushort.Parse(raw.AsSpan(i + 1, 4),
+                        NumberStyles.HexNumber, CultureInfo.InvariantCulture));
+                    i += 4;
+                    break;
+            }
+        }
+        return sb.ToString();
+    }
+
     /// <summary>The JSON string value, or null when the node is not a string.</summary>
     public static string? AsString(JsonNode? n)
     {
         if (n is JsonValue v)
         {
-            if (v.TryGetValue<string>(out var s)) return s;
+            if (JsVal.TryGetStringLenient(v, out var s)) return s;
             if (v.TryGetValue<JsonElement>(out var e) && e.ValueKind == JsonValueKind.String)
                 return e.GetString();
         }
@@ -180,7 +245,7 @@ public static string ToJsString(JsonNode? n)
             case JsonObject:
                 return "[object Object]";
             case JsonValue v:
-                if (v.TryGetValue<string>(out var s)) return s;
+                if (JsVal.TryGetStringLenient(v, out var s)) return s;
                 if (v.TryGetValue<bool>(out var b)) return b ? "true" : "false";
                 var num = AsNumber(n);
                 if (num.HasValue) return JsNumberToString(num.Value);