When backing out a character in a constructed string in JSON, first make sure

the string has not been reset by on OOM.

FossilOrigin-Name: 950bf9fe7829864e0abe6d71ca0495f346feb5d7943d76c95e55a6b86ea855da

Author: drh

manifest

@@ -1,5 +1,5 @@
-C wasm\sbuild:\sreformulate\san\sawk\sinvocation\sto\saccount\sfor\sawks\swhich\sdo\snot\ssupport\sthe\s-e\sflag.\sProblem\sreported\son\sthe\sforum\svia\sa\sdocker-hosted\sbuild.
-D 2024-01-16T14:28:59.125
+C When\sbacking\sout\sa\scharacter\sin\sa\sconstructed\sstring\sin\sJSON,\sfirst\smake\ssure\nthe\sstring\shas\snot\sbeen\sreset\sby\son\sOOM.
+D 2024-01-20T12:19:16.518
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md df5091916dbb40e6e9686186587125e1b2ff51f022cc334e886c19a0e9982724
@@ -697,7 +697,7 @@ F src/hash.h 3340ab6e1d13e725571d7cee6d3e3135f0779a7d8e76a9ce0a85971fa3953c51
 F src/hwtime.h f9c2dfb84dce7acf95ce6d289e46f5f9d3d1afd328e53da8f8e9008e3b3caae6
 F src/in-operator.md 10cd8f4bcd225a32518407c2fb2484089112fd71
 F src/insert.c 3f0a94082d978bbdd33c38fefea15346c6c6bffb70bc645a71dc0f1f87dd3276
-F src/json.c 4913fd22c4f0fa30643afb93a4d78d289cd490620e782b31016c3d4b2049b1cc
+F src/json.c fdb6b417e997d9b45ffd817c8c9d955dba11b99fa1199f8d03cb8fc5a9ee0941
 F src/legacy.c d7874bc885906868cd51e6c2156698f2754f02d9eee1bae2d687323c3ca8e5aa
 F src/loadext.c 7432c944ff197046d67a1207790a1b13eec4548c85a9457eb0896bb3641dfb36
 F src/main.c 438b95162acfa17b7d218f586f5bde11d6ae82bcf030c9611fc537556870ad6b
@@ -2157,14 +2157,9 @@ F vsixtest/vsixtest.tcl 6a9a6ab600c25a91a7acc6293828957a386a8a93
 F vsixtest/vsixtest.vcxproj.data 2ed517e100c66dc455b492e1a33350c1b20fbcdc
 F vsixtest/vsixtest.vcxproj.filters 37e51ffedcdb064aad6ff33b6148725226cd608e
 F vsixtest/vsixtest_TemporaryKey.pfx e5b1b036facdb453873e7084e1cae9102ccc67a0
-P 1066602b2b1976fe58b5150777cced894af17c803e068f5918390d6915b46e1d
-Q +5836657929d7d6d3f0d5865c9f6de4e4c00edd53d15a246802b375fa15d0f255
-R db1e652f52a6c391acbbefee0c13a4c1
-T *branch * branch-3.45
-T *sym-branch-3.45 *
-T -sym-release * Cancelled\sby\sbranch.
-T -sym-trunk * Cancelled\sby\sbranch.
-T -sym-version-3.45.0 * Cancelled\sby\sbranch.
-U stephan
-Z 763d16740affbc27389541de43d084d3
+P 90dd51153fd0a6197e2ee49b5492ad120f0bfc324b60651f3d4f47c286887b46
+Q +666690eb433fe38fa527ccbbb8e2c00041a33939da4f6b8bfb737d664f28f0d8
+R b92c7203f755b0af81ba067b0b4d09c9
+U drh
+Z 339bfa943d20e7905e6df807d394df8f
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-90dd51153fd0a6197e2ee49b5492ad120f0bfc324b60651f3d4f47c286887b46
+950bf9fe7829864e0abe6d71ca0495f346feb5d7943d76c95e55a6b86ea855da

src/json.c

@@ -589,14 +589,24 @@ static void jsonAppendChar(JsonString *p, char c){
   }
 }
 
+/* Remove a single character from the end of the string
+*/
+static void jsonStringTrimOneChar(JsonString *p){
+  if( p->eErr==0 ){
+    assert( p->nUsed>0 );
+    p->nUsed--;
+  }
+}
+
+
 /* Make sure there is a zero terminator on p->zBuf[]
 **
 ** Return true on success.  Return false if an OOM prevents this
 ** from happening.
 */
 static int jsonStringTerminate(JsonString *p){
   jsonAppendChar(p, 0);
-  p->nUsed--;
+  jsonStringTrimOneChar(p);
   return p->eErr==0;
 }
 
@@ -2260,7 +2270,7 @@ static u32 jsonTranslateBlobToText(
         j = jsonTranslateBlobToText(pParse, j, pOut);
         jsonAppendChar(pOut, ',');
       }
-      if( sz>0 ) pOut->nUsed--;
+      if( sz>0 ) jsonStringTrimOneChar(pOut);
       jsonAppendChar(pOut, ']');
       break;
     }
@@ -2274,7 +2284,7 @@ static u32 jsonTranslateBlobToText(
         jsonAppendChar(pOut, (x++ & 1) ? ',' : ':');
       }
       if( x & 1 ) pOut->eErr |= JSTRING_MALFORMED;
-      if( sz>0 ) pOut->nUsed--;
+      if( sz>0 ) jsonStringTrimOneChar(pOut);
       jsonAppendChar(pOut, '}');
       break;
     }
@@ -4402,7 +4412,7 @@ static void jsonArrayCompute(sqlite3_context *ctx, int isFinal){
       if( isFinal ){
         if( !pStr->bStatic ) sqlite3RCStrUnref(pStr->zBuf);
       }else{
-        pStr->nUsed--;
+        jsonStringTrimOneChar(pStr);
       }
       return;
     }else if( isFinal ){
@@ -4412,7 +4422,7 @@ static void jsonArrayCompute(sqlite3_context *ctx, int isFinal){
       pStr->bStatic = 1;
     }else{
       sqlite3_result_text(ctx, pStr->zBuf, (int)pStr->nUsed, SQLITE_TRANSIENT);
-      pStr->nUsed--;
+      jsonStringTrimOneChar(pStr);
     }
   }else{
     sqlite3_result_text(ctx, "[]", 2, SQLITE_STATIC);
@@ -4522,7 +4532,7 @@ static void jsonObjectCompute(sqlite3_context *ctx, int isFinal){
       if( isFinal ){
         if( !pStr->bStatic ) sqlite3RCStrUnref(pStr->zBuf);
       }else{
-        pStr->nUsed--;
+        jsonStringTrimOneChar(pStr);
       }
       return;
     }else if( isFinal ){
@@ -4532,7 +4542,7 @@ static void jsonObjectCompute(sqlite3_context *ctx, int isFinal){
       pStr->bStatic = 1;
     }else{
       sqlite3_result_text(ctx, pStr->zBuf, (int)pStr->nUsed, SQLITE_TRANSIENT);
-      pStr->nUsed--;
+      jsonStringTrimOneChar(pStr);
     }
   }else{
     sqlite3_result_text(ctx, "{}", 2, SQLITE_STATIC);