More work on the sahpool digest fix. New/fixed versions can read legacy (no digest) files but the reverse is only possible in limited circumstances (when files originated from a legacy version). The burning question is whether the real fix would be to remove this digest check altogether, as it only applies in a very limited context, and the fact that it was broken for some 18 months unnoticed suggests that its value might not be worth the CPU cycles.

FossilOrigin-Name: 0df62b776c68bebb0e187b353b6f29b0a41a29f0a1c8d6728fa6b9f7ce0d13f7

ext/wasm/api/sqlite3-vfs-opfs-sahpool.c-pp.js

@@ -79,23 +79,39 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
         capi.SQLITE_OPEN_MAIN_JOURNAL |
         capi.SQLITE_OPEN_SUPER_JOURNAL |
         capi.SQLITE_OPEN_WAL;
-  const FLAG_COMPUTE_DIGEST_V2 = 1 ? capi.SQLITE_OPEN_MEMORY : 0
+  const FLAG_COMPUTE_DIGEST_V2 = capi.SQLITE_OPEN_MEMORY
   /* Part of the fix for
      https://github.com/sqlite/sqlite-wasm/issues/97
 
-     Summary: prior to versions 3.49.1 and 3.50 computeDigest() always
-     computes a value of [0,0], so it does not actually do anything
-     useful.  Fixing it invalidates old persistent files, so we
-     instead only fix it for files created or updated since the bug
-     was discovered and fixed.
+     Summary: prior to versions 3.49.2 and 3.50.0 computeDigest()
+     always computes a value of [0,0] due to overflows, so it does not
+     do anything useful.  Fixing it invalidates old persistent files,
+     so we instead only fix it for files created or updated since the
+     bug was discovered and fixed.
 
      This flag determines whether we use the broken legacy
      computeDigest() or the v2 variant. We only use this flag for
      newly-created/overwritten files. Pre-existing files have the
      broken digest stored in them so need to continue to use that.
 
-     This flag is stored in the same space as the
-     SQLITE_OPEN_... flags and we must be careful here to not use an
+     What this means, in terms of db file compatibility between
+     versions:
+
+     - DBs created with versions older than this fix (<=3.49.1)
+     can be read by post-fix versions. Such DBs which are written
+     to in-place (not replaced) by newer versions can still be read
+     by older versions, as the affected digest is only modified
+     when the SAH slot is assigned to a given filename.
+
+     - DBs created with post-fix versions will, when read by a pre-fix
+     version, be seen as having a "bad digest" and will be
+     unceremoniously replaced by that pre-fix version. When swapping
+     back to a post-fix version, that version will see that the file
+     entry is missing the FLAG_COMPUTE_DIGEST_V2 bit so will treat it
+     as a legacy file.
+
+     This flag is stored in the same memory as the variour
+     SQLITE_OPEN_... flags and we must be careful here to not use a
      flag bit which is otherwise relevant for the VFS.
      SQLITE_OPEN_MEMORY is handled by sqlite3_open_v2() and friends,
      not the VFS, so we'll repurpose that one.  If we take a
@@ -659,7 +675,7 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
       const fileDigest = new Uint32Array(HEADER_DIGEST_SIZE / 4);
       sah.read(fileDigest, {at: HEADER_OFFSET_DIGEST});
       const compDigest = this.computeDigest(this.#apBody, flags);
-      console.warn("getAssociatedPath() flags",flags.toString(16), "compDigest", compDigest);
+      //warn("getAssociatedPath() flags",'0x'+flags.toString(16), "compDigest", compDigest);
       if(fileDigest.every((v,i) => v===compDigest[i])){
         // Valid digest
         const pathBytes = this.#apBody.findIndex((v)=>0===v);
@@ -691,16 +707,16 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
         toss("Path too long:",path);
       }
       if(path && flags){
-        /* When re-writing files, update their digest, if needed,
-           to v2. We continue to use v1 for the (!path) case
-           (empty files) because there's little reason not to
-           use a digest of 0 for empty entries. */
+        /* When creating or re-writing files, update their digest, if
+           needed, to v2. We continue to use v1 for the (!path) case
+           (empty files) because there's little reason not to use a
+           digest of 0 for empty entries. */
         flags |= FLAG_COMPUTE_DIGEST_V2;
       }
       this.#apBody.fill(0, enc.written, HEADER_MAX_PATH_SIZE);
       this.#dvBody.setUint32(HEADER_OFFSET_FLAGS, flags);
       const digest = this.computeDigest(this.#apBody, flags);
-      console.warn("setAssociatedPath(",path,") digest",digest);
+      //console.warn("setAssociatedPath(",path,") digest",digest);
       sah.write(this.#apBody, {at: 0});
       sah.write(digest, {at: HEADER_OFFSET_DIGEST});
       sah.flush();
@@ -725,18 +741,18 @@ globalThis.sqlite3ApiBootstrap.initializers.push(function(sqlite3){
        See the docs for FLAG_COMPUTE_DIGEST_V2 for more details.
     */
     computeDigest(byteArray, fileFlags){
-      let h1 = 0xdeadbeef;
-      let h2 = 0x41c6ce57;
       if( fileFlags & FLAG_COMPUTE_DIGEST_V2 ){
+        let h1 = 0xdeadbeef;
+        let h2 = 0x41c6ce57;
         for(const v of byteArray){
           h1 = Math.imul(h1 ^ v, 2654435761);
           h2 = Math.imul(h2 ^ v, 104729);
         }
+        return new Uint32Array([h1>>>0, h2>>>0]);
       }else{
         /* this is what the buggy legacy computation worked out to */
-        h1 = h2 = 0;
+        return new Uint32Array([0,0]);
       }
-      return new Uint32Array([h1>>>0, h2>>>0]);
     }
 
     /**

ext/wasm/tests/opfs/sahpool/digest-worker.js

@@ -48,7 +48,7 @@ const runTests = function(sqlite3, poolUtil){
       sql: "insert into t(a) values(?)",
       bind: n++
     });
-    log("Record count: ",db.selectValue("select count(*) from t"));
+    log(fname,"record count: ",db.selectValue("select count(*) from t"));
   }finally{
     db.close();
   }
@@ -59,7 +59,7 @@ const runTests = function(sqlite3, poolUtil){
       sql: "insert into t(a) values(?)",
       bind: n++
     });
-    log("Record count: ",db.selectValue("select count(*) from t"));
+    log(fname,"record count: ",db.selectValue("select count(*) from t"));
   }finally{
     db.close();
   }
@@ -74,15 +74,14 @@ const runTests = function(sqlite3, poolUtil){
       sql: "insert into t(a) values(?)",
       bind: n++
     });
-    log("Record count: ",db.selectValue("select count(*) from t"));
+    log(fname2,"record count: ",db.selectValue("select count(*) from t"));
   }finally{
     db.close();
   }
 };
 
 globalThis.sqlite3InitModule().then(async function(sqlite3){
-  log("sqlite3 version:",sqlite3.capi.sqlite3_libversion(),
-      sqlite3.capi.sqlite3_sourceid());
+  log("sqlite3 version:",sqlite3.version);
   const sahPoolConfig = {
     name: 'opfs-sahpool-digest',
     clearOnInit: false,

ext/wasm/tests/opfs/sahpool/digest.html

@@ -36,7 +36,7 @@
         ***********************************************************************
 
         This is a bugfix test for the OPFS SAHPool VFS. It requires setting up
-        a database created using v3.49.0 or older, then runnig it again with
+        a database created using v3.49.0 or older, then running it again with
         a newer version.
       */
       (function(){

manifest

@@ -1,5 +1,5 @@
-C Add\sa\stest\sapp\sto\sassist\sin\svalidating\sthe\sSAHPool\sdigest\scalculation\sfix.
-D 2025-02-03T17:21:54.248
+C More\swork\son\sthe\ssahpool\sdigest\sfix.\sNew/fixed\sversions\scan\sread\slegacy\s(no\sdigest)\sfiles\sbut\sthe\sreverse\sis\sonly\spossible\sin\slimited\scircumstances\s(when\sfiles\soriginated\sfrom\sa\slegacy\sversion).\sThe\sburning\squestion\sis\swhether\sthe\sreal\sfix\swould\sbe\sto\sremove\sthis\sdigest\scheck\saltogether,\sas\sit\sonly\sapplies\sin\sa\svery\slimited\scontext,\sand\sthe\sfact\sthat\sit\swas\sbroken\sfor\ssome\s18\smonths\sunnoticed\ssuggests\sthat\sits\svalue\smight\snot\sbe\sworth\sthe\sCPU\scycles.
+D 2025-02-26T03:03:08.171
 F .fossil-settings/empty-dirs dbb81e8fc0401ac46a1491ab34a7f2c7c0452f2f06b54ebb845d024ca8283ef1
 F .fossil-settings/ignore-glob 35175cdfcf539b2318cb04a9901442804be81cd677d8b889fcc9149c21f239ea
 F LICENSE.md e108e1e69ae8e8a59e93c455654b8ac9356a11720d3345df2a4743e9590fb20d
@@ -645,7 +645,7 @@ F ext/wasm/api/sqlite3-api-worker1.c-pp.js 5cc22a3c0d52828cb32aad8691488719f47d2
 F ext/wasm/api/sqlite3-license-version-header.js 0c807a421f0187e778dc1078f10d2994b915123c1223fe752b60afdcd1263f89
 F ext/wasm/api/sqlite3-opfs-async-proxy.js 3774befd97cd1a5e2895c8225a894aad946848c6d9b4028acc988b5d123475af
 F ext/wasm/api/sqlite3-vfs-helper.c-pp.js 3f828cc66758acb40e9c5b4dcfd87fd478a14c8fb7f0630264e6c7fa0e57515d
-F ext/wasm/api/sqlite3-vfs-opfs-sahpool.c-pp.js d1d17004bfee7a9159b56888b83345c6219262448297a81966faae4fd28f749c
+F ext/wasm/api/sqlite3-vfs-opfs-sahpool.c-pp.js c18540f86e2d10a48d67f933edb05e29a0e2c904dbdc996f3c765a8b63c49aea
 F ext/wasm/api/sqlite3-vfs-opfs.c-pp.js 9b86ca2d8276cf919fbc9ba2a10e9786033b64f92c2db844d951804dee6c4b4e
 F ext/wasm/api/sqlite3-vtab-helper.c-pp.js e809739d71e8b35dfe1b55d24d91f02d04239e6aef7ca1ea92a15a29e704f616
 F ext/wasm/api/sqlite3-wasm.c 6f9d8529072d072359cd22dc5dfb0572c524684686569cfbd0f9640d7619fc10
@@ -700,8 +700,8 @@ F ext/wasm/tester1.c-pp.js 005a94be87b888ca33aff130aeaef58045781ebfb92e559063d14
 F ext/wasm/tests/opfs/concurrency/index.html 657578a6e9ce1e9b8be951549ed93a6a471f4520a99e5b545928668f4285fb5e
 F ext/wasm/tests/opfs/concurrency/test.js d08889a5bb6e61937d0b8cbb78c9efbefbf65ad09f510589c779b7cc6a803a88
 F ext/wasm/tests/opfs/concurrency/worker.js 0a8c1a3e6ebb38aabbee24f122693f1fb29d599948915c76906681bb7da1d3d2
-F ext/wasm/tests/opfs/sahpool/digest-worker.js cdf4bb6dad5e274985e4b0022d0d85f9e782df03352044d8c7c22532845d7304
-F ext/wasm/tests/opfs/sahpool/digest.html 83d0c2f1dd6fe83e9088c603091514ac8549ee04a4632d8cc51d27fd094f05b3
+F ext/wasm/tests/opfs/sahpool/digest-worker.js f8320caaf6368ee8c59f259de5bebe68232f678390dc773ee61c466e171881dc
+F ext/wasm/tests/opfs/sahpool/digest.html 08122dabf8ef56ac7d40f43660e178811166842bb47b37cbb11003030bb9ce09
 F ext/wasm/wasmfs.make 68999f5bd8c489239592d59a420f8c627c99169bbd6fa16a404751f757b9f702
 F magic.txt 5ade0bc977aa135e79e3faaea894d5671b26107cc91e70783aa7dc83f22f3ba0
 F main.mk 8cfe182232ac7bbc87530792db6f31c09f2a2f35e9887d0412978746efe42ea9
@@ -2211,8 +2211,8 @@ F tool/version-info.c 3b36468a90faf1bbd59c65fd0eb66522d9f941eedd364fabccd7227350
 F tool/warnings-clang.sh bbf6a1e685e534c92ec2bfba5b1745f34fb6f0bc2a362850723a9ee87c1b31a7
 F tool/warnings.sh 49a486c5069de041aedcbde4de178293e0463ae9918ecad7539eedf0ec77a139
 F tool/win/sqlite.vsix deb315d026cc8400325c5863eef847784a219a2f
-P 9234c33f92d92bfddc6211c9c587f1072e70837c0ffe1416ef7d84d59bacd364
-R 176b17e8248aa3df480fb81ba267bf4c
+P a1e304b8020025cc73a658bd8c7697d59b4f3ad96cac0a3e36553a3207d13dc6
+R 428e6412102dca0ea6c390f44246e72c
 U stephan
-Z 9279d9607c28db362f757a9d03a072e6
+Z eddb8c14b5cfddbfe410d5840cc6ef5c
 # Remove this line to create a well-formed Fossil manifest.

manifest.uuid

@@ -1 +1 @@
-a1e304b8020025cc73a658bd8c7697d59b4f3ad96cac0a3e36553a3207d13dc6
+0df62b776c68bebb0e187b353b6f29b0a41a29f0a1c8d6728fa6b9f7ce0d13f7