ADFA-5405: Let templates reference each other - #1779
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Pebble's StringLoader treats the name it is handed as the template body, so a
cross-reference resolves to itself: {% include "nav.peb" %} renders the literal
text "nav.peb", with no exception and no log line. That caps the web server at
one self-contained template per page.
This loader resolves a name against Templates.name instead, so extends, include,
import and embed all work. A name with no row throws LoaderException naming it.
Not wired up yet -- the next commit switches the engine over to it.
The engine now loads through DatabaseTemplateLoader instead of StringLoader, so an author can build a page out of several Templates rows -- a layout to extend, a nav partial to include -- instead of one self-contained file. Content rows still name their outermost template by id, so render() resolves the id to a name and lets the engine load and cache from there. That drops our own compiled-template map: the engine already caches by name, which is the better key anyway, since a partial shared by many pages is then compiled once. Both caches are dropped on a database swap, the engine's included -- it caches by name, so a template edited under the same name would otherwise survive one. A reference to a name with no row now fails the request. It used to render the name as text.
Templates resolve by name now, so the bookshelf endpoint no longer has to look its id up and hold on to it: renderNamedTemplate takes the name straight. That removes the whole cache-coherency mechanism the cached id needed -- the volatile field, its lock, the generation it was tagged with, and the pre-serve refresh that existed only to make the generation check land on the right side of a swap. Nothing outside the content source caches per database any more, and the source applies a pending swap inside lookup()/withDatabase() itself. isCursorOneRow went with it; the id lookup was its only caller.
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WalkthroughThe change replaces template-ID compilation with name-based database resolution. Pebble loads referenced templates from SQLite by exact name. ChangesNamed Template Rendering
Estimated code review effort: 3 (Moderate) | ~20 minutes Merge Risk: ⚪ Minimal · up to Templates can now reference other database-backed templates by name, with bounded rendering and controlled error responses. No merge-blocking current-head risk remains. Sequence Diagram(s)sequenceDiagram
participant WebServer
participant DocumentationContentSource
participant DatabaseTemplateLoader
participant SQLiteDatabase
WebServer->>DocumentationContentSource: renderNamedTemplate("bookshelf", contextJson, path)
DocumentationContentSource->>DatabaseTemplateLoader: resolve template by name
DatabaseTemplateLoader->>SQLiteDatabase: query Templates by exact name
SQLiteDatabase-->>DatabaseTemplateLoader: return content blob or no row
DatabaseTemplateLoader-->>DocumentationContentSource: return reader or LoaderException
DocumentationContentSource-->>WebServer: return rendered bytes or TemplateRenderException
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Actionable comments posted: 1
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In `@app/src/main/java/com/itsaky/androidide/localWebServer/WebServer.kt`:
- Line 854: Update handleBsEndpoint’s renderNamedTemplate error path to pass the
caught LoaderException message, using e.message ?: "" as the sendError details
instead of only the generic bookshelf error text.
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app/src/main/java/com/itsaky/androidide/localWebServer/WebServer.ktapp/src/test/java/com/itsaky/androidide/localWebServer/WebServerTest.ktcommon/src/main/java/com/itsaky/androidide/documentation/DatabaseTemplateLoader.ktcommon/src/main/java/com/itsaky/androidide/documentation/DocumentationContentSource.ktcommon/src/test/java/com/itsaky/androidide/documentation/DatabaseTemplateLoaderTest.ktcommon/src/test/java/com/itsaky/androidide/documentation/DocumentationContentSourceTest.ktdocs/documentation-database.md
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handleBsEndpoint replaced the caught exception's message with generic text, so a bookshelf template the loader cannot resolve -- the row itself, or anything it references -- 500ed with nothing to identify it. The name is the whole point of failing loudly. The generic text stays as the fallback for an exception with no message. Found in review of #1779.
Review follow-ups on #1779. A cycle between two templates is reachable now that a reference resolves to another row, and Pebble has no cycle detection: it recurses until the stack ends. StackOverflowError is an Error, so every catch on the serving path passes it through and the client gets a closed socket with no status line. Raised as an IllegalStateException naming the template instead. The listener already survived this (the accept loop catches Throwable), so this is about the response. PebbleException formats getMessage() as "<text> (<file>:<line>)" and the loader throws with both null, so /pr/bs was answering "... not found in the database (?:?)". Translated to getPebbleMessage() in the content source, which also keeps Pebble out of both transports. clearTemplateCache() left the tag cache populated, so a template's {% cache %} blocks would outlive the database swap the rest of the method exists to handle. Dropped renderTemplate(): the id-keyed entry point had one caller, which the previous commit moved to renderNamedTemplate, and no test uses it. Said plainly in the KDoc that generation and refreshDatabase have no production reader. The regression test from the previous commit asserted the body contained "bookshelf", which the generic fallback text does too -- it passed with or without the fix. It now asserts the loader's own sentence, and fails without it.
The call it described, discardCachesIfDatabaseChanged(), was deleted two commits ago. The swap is applied by lookup()/withDatabase() inside the content source now, so a request reaching neither does not poll for one -- the opposite of what the comment led a reader to expect.
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Ran an Fixed
Not fixed, with reasonsThree findings rest on the claim that SQLite reads the quoted string as a column name, so the constraint is live. That disposes of:
Two more:
Two comment tidies also went in: the test-class KDoc describing 640 unit tests green across |
…nder Second review pass on #1779. The getPebbleMessage() change in 6e6d865 traded one diagnostic loss for another: it strips PebbleException's "(<file>:<line>)" suffix from every exception, not just the loader's null/null ones, so a syntax error in a template said what was wrong but not which template or line. Now conditional on the exception actually carrying neither. The new test fails without it with 'Unexpected token "EXECUTE_END"' and no template name. maxRenderedSize bounds output that grows without end -- a runaway loop stays at one frame, so the StackOverflowError guard never sees it and OutOfMemoryError is an Error every catch on this path misses. Pebble raises a PebbleException at the limit instead. Not covered by a test: exercising it means rendering 16M chars. clearTemplateCache() now takes the write lock. The sentinel and the interceptor call it with no lock, so clearing three caches piecemeal under a concurrent render could hand it a template from before the clear and a tag-cache miss from after -- the mixed state the sentinel is pressed to escape. resourceExists() no longer copies the whole template blob into a CursorWindow to answer a boolean, and generation/refreshDatabase() are marked @VisibleForTesting rather than described as unused in prose. The Templates DDL is now in documentation-database.md. Two reviews read the bare column list there and concluded name has no UNIQUE constraint; it does -- SQLite resolves the single-quoted UNIQUE('name') to the column.
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Second Fixed
Two corrections to the finding text, since both matter for whether the fix is right:
Not fixedThe three Two independent reviews reaching the same wrong conclusion from the same doc is a defect in the doc, not in the reviews — so cdaf2da puts the DDL and that One correction to my previous reply: I wrote that the null/empty/duplicate count is "0 on the shipped database". I queried a local Remaining two:
Also declined: keying the loader on an id-shaped 641 unit tests green across |
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Filed ADFA-5468 for the error-echo point rather than fixing it here. Checking the siblings turned up four sites, not the three I described above — The ticket flags that line 780's echo is intentional and pinned by a regression test here, so whoever picks it up keeps that behavior rather than reverting it. |
| // | ||
| // Headroom over the largest context this database holds (171 KB of compressed JSON), not a | ||
| // measured ceiling on rendered output; tighten it if the real maximum is known. | ||
| private const val MAX_RENDERED_CHARS = 16 * 1024 * 1024 |
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@davidschachterADFA MAX_RENDERED_CHARS is too large to fire before the OOM it exists to prevent.
The comment says the cap is here because a runaway {% for %} "grows the writer until the heap gives out, and OutOfMemoryError is an Error every catch on this path misses." At 16 MiB the guard doesn't reach that far on-device.
Pebble enforces the limit in LimitedSizeWriter, which wraps the StringWriter in renderNamed. To trip it, the underlying StringBuffer must reach 16.7M chars — a 33.5 MB char[]. The doubling step immediately before that holds the 33.5 MB old array and the 67 MB new one at once (~100 MB transient), and if the render does complete, .toString() copies another 33.5 MB and .toByteArray() another 16–50 MB.
On a phone with a 192–256 MB heap, the runaway loop OOMs well before 16.7M chars — exactly the scenario the constant exists for. The comment itself notes the number is headroom over a 171 KB context rather than a measured ceiling on rendered output; the two aren't related. Something around 1 MiB would both actually fire and still sit ~6x above any legitimate rendered page.
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You're right, and the arithmetic is the part I hadn't done. Changed to 1 MiB in 4e2e61984.
I checked your reasoning rather than just taking it: Pebble's maxRenderedSize counts characters in LimitedSizeWriter, so 16 Mi chars is a 33.5 MB char[], the doubling step that reaches it holds the 33.5 MB old array and the 67 MB new one simultaneously, and toString() copies another 33.5 MB. Against a 192-256 MB heap the runaway loop OOMs well before the guard fires — so the guard was decorative in exactly the scenario it was written for.
You also put your finger on how it got that value: the comment sized it as headroom over the largest context in the database (171 KB of compressed JSON), which has nothing to do with rendered output size. It said as much and I still left the number. The new comment records the character-vs-byte arithmetic and why 1 MiB was chosen, so the next person doesn't have to re-derive it:
1 MiB of characters is ~2 MB of
char[]and still roughly 6x the largest legitimate rendered page here, so it bounds the runaway without being reachable by real content.
If you know the real maximum rendered page in the shipping database I'll tighten it further — 1 MiB is a defensible bound, not a measured one.
All three findings hold. The first one is not fully fixed by what it
suggested, which is the interesting part.
The echoed message is narrowed, and there was a second site. The
suggestion was to give render failures a distinct type and echo only
those; TemplateRenderException does that, extending IllegalStateException
so callers that only care the render failed are unaffected. But narrowing
handleBsEndpoint's catch does not stop the leak: realHandleBsEndpoint has
its own catch around bookshelfJson which calls sendError with e.message
and returns null, so the outer catch never sees the exception. That inner
site is where a SQLiteException's SQL and withDatabase's check() failure --
which names the database file -- were actually reaching the client. Both
are closed now. The regression test fails against the first fix alone,
which is how the second site turned up.
MAX_RENDERED_CHARS drops from 16 MiB to 1 MiB. The arithmetic in the
finding is right: Pebble counts characters, so 16 Mi chars is a 33.5 MB
char[], the doubling that reaches it holds 33.5 MB and 67 MB at once, and
toString() copies another 33.5 MB. Against a 192-256 MB heap the runaway
loop OOMs long before the guard fires -- the one case it exists for. The
old number was headroom over the largest context in the database, which is
an unrelated quantity, as its own comment conceded. 1 MiB still sits well
above any legitimate rendered page here.
clearTemplateCache carries swapDatabaseIfChanged's warning. It takes the
write lock, withDatabase runs its block under the read lock, and
ReentrantReadWriteLock does not upgrade -- so withDatabase {
clearTemplateCache() } deadlocks permanently. Latent: all four current
callers are outside the read lock. The note is what keeps the next one out.
Separately, and NOT fixed here: sendError echoes e.message on two general
request paths too (WebServer.kt around the request-processing catch, and
the DocumentationLookup.Failed branch). Same exposure, any content path
rather than just /pr/bs, and pre-existing rather than introduced by this
ticket -- so it wants its own change, not a quiet widening of this one.
Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Gw89A3KWsPtvgPYtXYLBwr
2 participants
Templates in the
Templatestable can now reference each other, so an author can build a page out of a layout, a nav partial and a page body instead of one self-contained file. ADFA-5405Why it didn't work
The engine was built with Pebble's
StringLoader, which treats the name it is handed as the template body, and it was handed each template's source as its name. So every cross-reference resolved to itself:{% include "nav.peb" %}asked the loader fornav.peb, got those eight characters back as a template, and the page rendered the literal text. No exception, no log line.page.pebandnav.pebwork around this today by defining local macros rather than including each other.The change
DatabaseTemplateLoaderresolves a name againstTemplates.name, soextends,include,importandembedall work.Contentrows still name their outermost template by id;renderresolves that id to a name and the engine loads and caches from there — which drops our own compiled-template map, since the engine already caches by name. Name is the better key anyway: a partial shared by many pages is compiled once. Both caches are dropped on a database swap, the engine's included.No schema change and no new dependency: the database already holds four named templates, and Pebble 4.1.1 already exposes the loader interface.
A reference to a name with no row now fails the request naming the template, rather than rendering the name as text.
Review by commit
docs/documentation-database.md.Verification
637 unit tests green across
:commonand:app; Spotless clean. Four new tests coverinclude,extends, a missing reference, and a named render; three existing template tests were updated for the id-to-name lookup.On a Pixel 6 Pro, against a debug
documentation.dbcarrying three cross-referencing templates:extendsa layout andincludes a nav partial200—<main>Hello Kotlin! [nav:Kotlin]</main>500—Template 'e2e-nowhere' not found in the database200, unchanged/pr/bs(bookshelf, now rendered by name)200, unchanged🤖 Generated with Claude Code