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fix(terminal): read iTerm2 pictures past xterm's 10M string handler cap - #3170
With Settings > Terminal > Pictures in the terminal on, src/lib/itermPictures.ts read iTerm2 OSC 1337 payloads through terminal.parser.registerOscHandler, which is a string handler. xterm stops holding a string payload at 10,000,000 characters (PAYLOAD_LIMIT) and then does not call the handler at all. So a single-part File= picture of about 7.5 MB or more went to @xterm/addon-image unchanged. The addon drops both kinds the pre-handler exists for, so nothing was drawn:
a picture with no size= (as chafa -f iterm sends), or
a TIFF picture.
Reproduced on origin/main 3962f0f with a real xterm 6.0.0 Terminal and a string handler on 1337: called for 1,000 and 9,999,000 base64 characters, not called for 10,000,008.
What changed
itermPictures now also returns stream, a streaming handler (start/put/end) like the addon's own decoders. It holds a payload up to the addon's size cap (iipSizeLimit, plus room for the arguments) and at the end hands it to the same handle logic as before. It stops holding a payload as soon as its start shows the addon reads it as it comes (a File= with size= that is not a TIFF, or any other OSC 1337 command). That payload ends with false, so the addon reads it as before, and no second copy is held. A payload past the cap is dropped, as the addon would drop it, and so is a FilePart= with no multipart picture coming in. The pieces are joined a thousand at a time, so a payload fed in tiny pieces does not cost one string per piece, and the parser's code points are turned into text with String.fromCodePoint, so arguments with characters past U+FFFF read as they did through the string handler.
terminalImages.ts: registerOscStream registers a streaming handler on xterm's own parser (_core._inputHandler._parser), the same place the addon registers its handlers. Where that parser is missing (another xterm version), the string handler is registered as before.
The handler that swallows pictures while the setting is off uses the same streaming registration. Before, a picture past 10,000,000 characters got past it and was drawn even with the setting off. That was already true for large PNGs with size=; without this change it would also have been true for the TIFFs this PR now reads.
I did not take the issue's other option (capping the addon's iipSizeLimit at 7.5 MB): on desktop it would stop drawing PNG and JPEG pictures between 7.5 MB and 20 MB that are drawn today.
No new control or setting; this only changes how an existing opt-in setting reads its input.
Validation
New test in src/lib/itermPictures.test.ts: on a real xterm Terminal, a 2048 x 1280 RGBA TIFF (about 14 million base64 characters, no size=) written as one File= payload comes out as a PNG of the same pixels. A PNG with size= and more than 10,000,000 characters is left to the handler behind it (the addon's place) and not fed here. On main this file fails (no streaming handler to register).
A second new unit test feeds a payload in 7-code-point pieces, with a 5,000-character argument and a character past U+FFFF: same result as the whole payload.
scripts/terminal-images-demo-regression.ts gets a step that prints a 1700 x 1700 chafa-layout TIFF (about 15 million base64 characters) in the demo build. It fails on main (actual: null) and passes here.
bun scripts/terminal-ghostty-demo-regression.ts: PASS.
bun test src/lib/itermPictures.test.ts src/lib/ghostty/overlay.test.ts: 15 pass.
Before opening, a Codex (Terra, xhigh) adversarial pass found no HIGH. Its MEDIUM (one held string per put, so many small pieces cost about 10x their text) and two LOWs (a header longer than 4,096 characters split at that point went to the addon; characters past U+FFFF were truncated) are fixed above.
bun run check fast on the branch (P620, before merging 3 unrelated main commits): workflow syntax, generated types/themes, typecheck, build, unit tests all ok. After the merge: bun run typecheck ok.
Review round (Codex Terra xhigh on 38e822e; omo was CLEAR there): no HIGH. Fixed in 7183a22: (MEDIUM) the cap counted the arguments too, so a picture at the phone cap with more than 4,096 characters of arguments was dropped where the addon reads it; the cap is now on the base64 after the colon, and up to 64 KiB of arguments are read to tell a payload's kind. (LOW) a payload that began while the setting was off was still held until its end; now it is not held. New unit test for the first; it fails on 38e822e. bun run check fast on 7183a22: all ok.
Not changed: where xterm's internal parser is missing, the fallback string handler keeps xterm's 10,000,000-character limit, as before this PR (the addon itself needs that parser).
Skipped: the integration suite and browser lanes other than the two terminal picture regressions above (CI runs them).
xterm does not call a string OSC handler for a payload past 10,000,000
characters, so a single-part File= picture of 7.5 MB or more without
size=, or a TIFF, went to the image addon unchanged and was not drawn.
The pictures handler is now a streaming handler on xterm's own parser,
as the addon's decoders are, holding a payload up to the addon's cap.
Pictures the addon reads as they come are not held. The handler that
swallows pictures while the setting is off streams too, so a picture
past the cap is not drawn then either.
Fixes#3154.
Improved handling of large terminal image payloads, including TIFF images that exceed the terminal’s usual string-size limit.
Image data is now handled more reliably when it arrives in small chunks or contains supplementary Unicode characters.
Image size limits are applied to the encoded image data, helping prevent valid payloads from being rejected because of unrelated metadata.
The iTerm2 picture handler now processes OSC 1337 payloads incrementally, including payloads beyond xterm’s 10,000,000-character string-handler limit. Terminal image handling uses xterm streaming registration when available and retains a whole-payload fallback.
The picture handler adds an OSC stream interface with bounded buffering, addon pass-through, and a base64 size check. Tests cover chunked input, supplementary Unicode characters, and size-limit behavior.
xterm stream registration and regression coverage src/lib/terminalImages.ts, src/lib/itermPictures.test.ts, scripts/terminal-images-demo-regression.ts
Terminal image handling registers the stream handler when available and uses whole-payload handling as a fallback. Tests and the demo regression cover large TIFF payloads and addon pass-through.
devswha/ovis#2871: Adds iTerm2 picture rendering and the disabled-picture handler that this change updates for streaming.
devswha/ovis#3035: Adds iTerm2 picture sequence detection and xterm drawing integration related to the handler updated here.
Merge Risk: Low · up to 7183a
The change is mergeable with awareness of a narrow edge case: a valid near-limit image with unusually long arguments can be discarded. Tracking the actual argument boundary would remove that limitation.
Pre-merge checks: 4 · 1
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Title check
The title identifies the fix for iTerm2 pictures that exceed xterm's string-handler limit.
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The description covers the problem, changes, validation results, and skipped checks. To match the template, combine the change sections under the heading “Change”.
Linked Issues check
[#3154] The streaming handler receives large single-part pictures and sends pictures without size= or TIFF pictures to the existing pre-handler. The real-xterm test checks a TIFF above 10 million ba…
Out of Scope Changes check
[#3154] Streaming registration, disabled-setting handling, and the regression tests support the picture-handling change. The demo regression exercises the reported large-TIFF case.
Full details: Linked Issues check
Explanation
[#3154] The streaming handler receives large single-part pictures and sends pictures without size= or TIFF pictures to the existing pre-handler. The real-xterm test checks a TIFF above 10 million base64 characters. Tests also cover streaming chunks, size limits, and pass-through to the downstream handler.
Full details: Docstring Coverage
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… hold none while off
Review round on #3170: a picture at the phone cap with arguments past
4,096 characters was dropped where the addon would read it, and a
payload that began while the setting was off was still held until its
end.
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Actionable comments posted: 1
Fix comments: Fix CodeRabbit comments on this PR
Prompt to fix all issues
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Inline comments:
Review comments at @src/lib/itermPictures.ts:
- Around line 305-321: Update the put handler’s argument-boundary tracking so
arguments longer than ARGS_ROOM are not counted toward the image-size cap;
detect the actual colon position from incoming data even when it falls beyond
head’s buffer. Ensure leftToAddon can inspect the image prefix after the full
arguments, so near-limit PNG data is passed to the addon rather than dropped.
---
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Reviewing files that changed from the base of the PR and between ade0589 and 7183a22.
Files selected for processing: 4
scripts/terminal-images-demo-regression.ts
src/lib/itermPictures.test.ts
src/lib/itermPictures.ts
src/lib/terminalImages.ts
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omo (dori review): CLEAR on 38e822e and again on 7183a22.
Codex (Terra, xhigh), pass 1 before opening: no HIGH. MEDIUM (one held string per put) and two LOWs (a header split at 4,096 characters; characters past U+FFFF truncated): fixed in the first commit.
Codex pass 2 on 38e822e: no HIGH. MEDIUM (arguments counted toward the cap at the phone limit) and LOW (held while the setting is off): fixed in 7183a22, with a unit test that fails on 38e822e.
CodeRabbit: one Minor (arguments longer than 65,536 characters). Left as is, with the reason in the thread. Remaining LOWs, not fixed: that one, and the fallback when xterm's internal parser is missing keeps the old 10,000,000-character limit, as before this PR.
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Fixes #3154 (follow-up of #3150).
What was wrong
With Settings > Terminal > Pictures in the terminal on,
src/lib/itermPictures.tsread iTerm2 OSC 1337 payloads throughterminal.parser.registerOscHandler, which is a string handler. xterm stops holding a string payload at 10,000,000 characters (PAYLOAD_LIMIT) and then does not call the handler at all. So a single-partFile=picture of about 7.5 MB or more went to@xterm/addon-imageunchanged. The addon drops both kinds the pre-handler exists for, so nothing was drawn:size=(aschafa -f itermsends), orReproduced on origin/main 3962f0f with a real xterm 6.0.0
Terminaland a string handler on 1337: called for 1,000 and 9,999,000 base64 characters, not called for 10,000,008.What changed
itermPicturesnow also returnsstream, a streaming handler (start/put/end) like the addon's own decoders. It holds a payload up to the addon's size cap (iipSizeLimit, plus room for the arguments) and at the end hands it to the samehandlelogic as before. It stops holding a payload as soon as its start shows the addon reads it as it comes (aFile=withsize=that is not a TIFF, or any other OSC 1337 command). That payload ends withfalse, so the addon reads it as before, and no second copy is held. A payload past the cap is dropped, as the addon would drop it, and so is aFilePart=with no multipart picture coming in. The pieces are joined a thousand at a time, so a payload fed in tiny pieces does not cost one string per piece, and the parser's code points are turned into text withString.fromCodePoint, so arguments with characters past U+FFFF read as they did through the string handler.terminalImages.ts:registerOscStreamregisters a streaming handler on xterm's own parser (_core._inputHandler._parser), the same place the addon registers its handlers. Where that parser is missing (another xterm version), the string handler is registered as before.size=; without this change it would also have been true for the TIFFs this PR now reads.I did not take the issue's other option (capping the addon's
iipSizeLimitat 7.5 MB): on desktop it would stop drawing PNG and JPEG pictures between 7.5 MB and 20 MB that are drawn today.No new control or setting; this only changes how an existing opt-in setting reads its input.
Validation
src/lib/itermPictures.test.ts: on a real xtermTerminal, a 2048 x 1280 RGBA TIFF (about 14 million base64 characters, nosize=) written as oneFile=payload comes out as a PNG of the same pixels. A PNG withsize=and more than 10,000,000 characters is left to the handler behind it (the addon's place) and not fed here. On main this file fails (no streaming handler to register).scripts/terminal-images-demo-regression.tsgets a step that prints a 1700 x 1700 chafa-layout TIFF (about 15 million base64 characters) in the demo build. It fails on main (actual: null) and passes here.bun scripts/terminal-ghostty-demo-regression.ts: PASS.bun test src/lib/itermPictures.test.ts src/lib/ghostty/overlay.test.ts: 15 pass.put, so many small pieces cost about 10x their text) and two LOWs (a header longer than 4,096 characters split at that point went to the addon; characters past U+FFFF were truncated) are fixed above.bun run check faston the branch (P620, before merging 3 unrelated main commits): workflow syntax, generated types/themes, typecheck, build, unit tests all ok. After the merge:bun run typecheckok.bun run check faston 7183a22: all ok.