Index: src/json.c
==================================================================
--- src/json.c
+++ src/json.c
@@ -618,10 +618,44 @@
   if( p->nUsed==0 ) return;
   c = p->zBuf[p->nUsed-1];
   if( c=='[' || c=='{' ) return;
   jsonAppendChar(p, ',');
 }
+
+/* c is a control character.  Append the canonical JSON representation
+** of that control character to p.
+**
+** This routine assumes that the output buffer has already been enlarged
+** sufficiently to hold the worst-case encoding plus a nul terminator.
+*/
+static void jsonAppendControlChar(JsonString *p, u8 c){
+  static const char aSpecial[] = {
+     0, 0, 0, 0, 0, 0, 0, 0, 'b', 't', 'n', 0, 'f', 'r', 0, 0,
+     0, 0, 0, 0, 0, 0, 0, 0,   0,   0,   0, 0,   0,   0, 0, 0
+  };
+  assert( sizeof(aSpecial)==32 );
+  assert( aSpecial['\b']=='b' );
+  assert( aSpecial['\f']=='f' );
+  assert( aSpecial['\n']=='n' );
+  assert( aSpecial['\r']=='r' );
+  assert( aSpecial['\t']=='t' );
+  assert( c>=0 && c<sizeof(aSpecial) );
+  assert( p->nUsed+7 <= p->nAlloc );
+  if( aSpecial[c] ){
+    p->zBuf[p->nUsed] = '\\';
+    p->zBuf[p->nUsed+1] = aSpecial[c];
+    p->nUsed += 2;
+  }else{
+    p->zBuf[p->nUsed] = '\\';
+    p->zBuf[p->nUsed+1] = 'u';
+    p->zBuf[p->nUsed+2] = '0';
+    p->zBuf[p->nUsed+3] = '0';
+    p->zBuf[p->nUsed+4] = "0123456789abcdef"[c>>4];
+    p->zBuf[p->nUsed+5] = "0123456789abcdef"[c&0xf];
+    p->nUsed += 6;
+  }
+}
 
 /* Append the N-byte string in zIn to the end of the JsonString string
 ** under construction.  Enclose the string in double-quotes ("...") and
 ** escape any double-quotes or backslash characters contained within the
 ** string.
@@ -678,39 +712,18 @@
       z += k;
       N -= k;
     }
     c = z[0];
     if( c=='"' || c=='\\' ){
-      json_simple_escape:
       if( (p->nUsed+N+3 > p->nAlloc) && jsonStringGrow(p,N+3)!=0 ) return;
       p->zBuf[p->nUsed++] = '\\';
       p->zBuf[p->nUsed++] = c;
     }else if( c=='\'' ){
       p->zBuf[p->nUsed++] = c;
     }else{
-      static const char aSpecial[] = {
-         0, 0, 0, 0, 0, 0, 0, 0, 'b', 't', 'n', 0, 'f', 'r', 0, 0,
-         0, 0, 0, 0, 0, 0, 0, 0,   0,   0,   0, 0,   0,   0, 0, 0
-      };
-      assert( sizeof(aSpecial)==32 );
-      assert( aSpecial['\b']=='b' );
-      assert( aSpecial['\f']=='f' );
-      assert( aSpecial['\n']=='n' );
-      assert( aSpecial['\r']=='r' );
-      assert( aSpecial['\t']=='t' );
-      assert( c>=0 && c<sizeof(aSpecial) );
-      if( aSpecial[c] ){
-        c = aSpecial[c];
-        goto json_simple_escape;
-      }
       if( (p->nUsed+N+7 > p->nAlloc) && jsonStringGrow(p,N+7)!=0 ) return;
-      p->zBuf[p->nUsed++] = '\\';
-      p->zBuf[p->nUsed++] = 'u';
-      p->zBuf[p->nUsed++] = '0';
-      p->zBuf[p->nUsed++] = '0';
-      p->zBuf[p->nUsed++] = "0123456789abcdef"[c>>4];
-      p->zBuf[p->nUsed++] = "0123456789abcdef"[c&0xf];
+      jsonAppendControlChar(p, c);
     }
     z++;
     N--;
   }
   p->zBuf[p->nUsed++] = '"';
@@ -1407,11 +1420,14 @@
       k = j+sz;
       while( j<k ){
         if( !jsonIsOk[z[j]] && z[j]!='\'' ){
           if( z[j]=='"' ){
             if( x==JSONB_TEXTJ ) return j+1;
-          }else if( z[j]!='\\' || j+1>=k ){
+          }else if( z[j]<=0x1f ){
+            /* Control characters in JSON5 string literals are ok */
+            if( x==JSONB_TEXTJ ) return j+1;
+          }else if( NEVER(z[j]!='\\') || j+1>=k ){
             return j+1;
           }else if( strchr("\"\\/bfnrt",z[j+1])!=0 ){
             j++;
           }else if( z[j+1]=='u' ){
             if( j+5>=k ) return j+1;
@@ -1701,13 +1717,18 @@
         }else{
           pParse->iErr = j;
           return -1;
         }
       }else if( c<=0x1f ){
-        /* Control characters are not allowed in strings */
-        pParse->iErr = j;
-        return -1;
+        if( c==0 ){
+          pParse->iErr = j;
+          return -1;
+        }
+        /* Control characters are not allowed in canonical JSON string
+        ** literals, but are allowed in JSON5 string literals. */
+        opcode = JSONB_TEXT5;
+        pParse->hasNonstd = 1;
       }else if( c=='"' ){
         opcode = JSONB_TEXT5;
       }
       j++;
     }
@@ -2184,11 +2205,11 @@
       u32 k;
       u32 sz2 = sz;
       zIn = (const char*)&pParse->aBlob[i+n];
       jsonAppendChar(pOut, '"');
       while( sz2>0 ){
-        for(k=0; k<sz2 && zIn[k]!='\\' && zIn[k]!='"'; k++){}
+        for(k=0; k<sz2 && (jsonIsOk[(u8)zIn[k]] || zIn[k]=='\''); k++){}
         if( k>0 ){
           jsonAppendRawNZ(pOut, zIn, k);
           if( k>=sz2 ){
             break;
           }
@@ -2196,10 +2217,17 @@
           sz2 -= k;
         }
         if( zIn[0]=='"' ){
           jsonAppendRawNZ(pOut, "\\\"", 2);
           zIn++;
+          sz2--;
+          continue;
+        }
+        if( zIn[0]<=0x1f ){
+          if( pOut->nUsed+7>pOut->nAlloc && jsonStringGrow(pOut,7) ) break;
+          jsonAppendControlChar(pOut, zIn[0]);
+          zIn++;
           sz2--;
           continue;
         }
         assert( zIn[0]=='\\' );
         assert( sz2>=1 );

Index: test/json501.test
==================================================================
--- test/json501.test
+++ test/json501.test
@@ -303,7 +303,34 @@
 # 2023-11-08 forum/forumpost/ddcad3e884
 #
 do_execsql_test 13.1 {
   SELECT json('{x:''a "b" c''}');
 } {{{"x":"a \"b\" c"}}}
+
+# 2024-01-31
+# Allow control characters within JSON5 string literals.
+#
+for {set c 1} {$c<=0x1f} {incr c} {
+  do_execsql_test 14.$c.1 {
+    SELECT json_valid('"abc' || char($c) || 'xyz"');
+  } {0}
+  do_execsql_test 14.$c.2 {
+    SELECT json_valid('"abc' || char($c) || 'xyz"', 2);
+  } {1}
+  switch $c {
+    8   {set e "\\b"}
+    9   {set e "\\t"}
+    10  {set e "\\n"}
+    12  {set e "\\f"}
+    13  {set e "\\r"}
+    default {set e [format "\\u00%02x" $c]}
+  }
+  do_execsql_test 14.$c.3 {
+    SELECT json('{label:"abc' || char($c) || 'xyz"}');
+  } "{{\"label\":\"abc${e}xyz\"}}"
+  do_execsql_test 14.$c.4 {
+    SELECT jsonb('{label:"abc' || char($c) || 'xyz"}') -> '$';
+  } "{{\"label\":\"abc${e}xyz\"}}"
+}
+
 
 finish_test