[mitchellh]

File transmissions with exactly S bytes or trailing file data previously failed because appendRemaining reports StreamTooLong when it reaches its limit. This broke the protocol's partial-file transmission path.

Use an exact-length allocation and read when S is nonzero, rejecting premature EOF and values above the image limit. Preserve the existing bounded read-to-EOF behavior for S=0.

https://sw.kovidgoyal.net/kitty/graphics-protocol/#local-client

[mitchellh]

Verification:

#!/usr/bin/env bash
set -euo pipefail

# KGP-06: S must select exactly that many bytes from a regular file.
# The file contains a red RGB pixel followed by a green RGB pixel. S=3 means
# the terminal must read only the red pixel; reading all six bytes is invalid
# for the declared 1x1 RGB image.

tty=/dev/tty
data_file="/tmp/kitty-graphics-protocol-kgp06.$$"
image_id=4242006
in_alt_screen=0
exec 3<>"$tty"

cleanup() {
    trap - EXIT HUP INT TERM
    if [ "$in_alt_screen" -eq 1 ]; then
        printf '\033_Ga=d,d=I,i=%s,q=2\033\\' "$image_id" >&3 || true
        printf '\033[?1049l' >&3 || true
    fi
    rm -f "$data_file"
}
trap cleanup EXIT HUP INT TERM

# This is one red RGB pixel followed by one green RGB pixel:
# ff 00 00 00 ff 00.
printf '\377\000\000\000\377\000' >"$data_file"
actual_size=$(wc -c <"$data_file" | tr -d ' ')
if [ "$actual_size" -ne 6 ]; then
    printf 'FAIL: fixture is %s bytes instead of 6\n' "$actual_size" >&2
    exit 1
fi
encoded_path=$(printf '%s' "$data_file" | base64 | tr -d '\r\n')

# Use a known screen position so running at the bottom of a terminal cannot
# immediately scroll the placement away.
printf '\033[?1049h\033[2J\033[H' >"$tty"
in_alt_screen=1
printf 'KGP-06: file contains red + green pixels; S=3 selects red.\n' >&3
printf 'Expected: a solid red 10x3-cell rectangle below.\n' >&3
printf '\033[3;1H' >&3

# Read the response ourselves so it does not end up in the shell input buffer.
printf '\033_Ga=T,f=24,t=f,s=1,v=1,S=3,O=0,i=%s,c=10,r=3,C=1;%s\033\\' \
    "$image_id" "$encoded_path" >&3
response=
while IFS= read -r -s -n 1 -t 10 char <&3; do
    response+="$char"
    if [[ "$response" == *$'\033\\' ]]; then
        break
    fi
done

printf '\033[7;1H' >&3
case "$response" in
    *';OK'*)
        printf 'PASS: terminal accepted exactly S=3 bytes.\n' >&3
        ;;
    '')
        printf 'FAIL: terminal did not send a graphics response.\n' >&3
        ;;
    *)
        printable=$(printf '%s' "$response" | LC_ALL=C tr -cd '\11\12\15\40-\176')
        printf 'FAIL: terminal response: %s\n' "$printable" >&3
        ;;
esac

printf 'Press Enter to remove the image and return to the previous screen...' >&3
IFS= read -r _ <&3