termrender

Overview ¶

Package termrender replays captured terminal output and writes the resulting text, line by line, to an output writer.

It exists to render the stdout/stderr a CI step produced into the text a human would have seen. A naive ANSI strip is not enough: tools like Docker redraw progress with carriage returns and cursor movement, so stripping the escapes alone leaves a pile of stale, half-drawn lines. Replaying the stream through a terminal model collapses those redraws to their final state.

Two rendering modes are offered:

• Render writes plain text — SGR styling is discarded. Use it when piping to a file or another program (grep/awk/less), where escape codes are noise.
• RenderStyled preserves SGR styling (colors, bold, underline, …): each rendered cell keeps the graphic rendition active when it was drawn, with redraws still collapsed. Use it for a human-facing viewer such as the interactive output pager.

Unlike a general terminal emulator it is built for the one job of rendering a (potentially enormous) append-only log:

• Lines are never wrapped. Each row holds a full logical line of unbounded width, so long log lines survive intact for grep/awk and friends. A fixed-width grid would either wrap (inserting fake breaks) or truncate them.
• Lines are streamed out as they scroll off the top of a fixed-height window, so memory stays flat (O(window)) and nothing is ever silently dropped, however large the log.
• There is no input/reply channel: device-status and color queries in the stream are simply ignored. The renderer never blocks waiting to answer them.

Cursor addressing is tracked in columns of one cell per rune; wide-rune (CJK) alignment inside an in-place redraw is therefore approximate, which is immaterial for the ASCII and box-drawing output that progress redraws use in practice.