`-read_timeout 0` does not disable the read timeout; only a negative value works (contradicts flag help)

[Robbie1977]

Summary

The -read_timeout flag help states "zero or negative value means no timeout", but passing 0 does not disable the timeout — the built-in 15s default is applied instead. Only a negative value (e.g. -1s) actually disables it. -write_timeout is unaffected only because its default is already 0.

Environment

• Version: v2 (branch v2), reproduced with the mayth/simple-upload-server image
• Docker, Linux

Expected

Per the flag help, -read_timeout 0 should disable the read timeout (map to http.Server.ReadTimeout = 0, which Go treats as no timeout), consistent with -write_timeout 0.

Actual

0 is treated as "unset" and replaced by the 15s default. Startup logs:

# no -read_timeout flag
config from flag:   ReadTimeout:0
merged flag config: ReadTimeout:15000000000
configured:         ReadTimeout:15s

# -read_timeout=0  (explicit) -> still 15s

# -read_timeout=-1s
configured:         ReadTimeout:-1s        # works: no timeout

Consequence: any upload whose body transfer exceeds 15s is cut mid-stream — the handler's r.FormFile read fails with failed to obtain form file: ... i/o timeout and returns 500 — making large uploads (multi-GB over ordinary links) impossible unless the operator discovers the undocumented -1s workaround.

Root cause

In app.go, ParseConfig builds configFromFlags and merges it over DefaultConfig:

config := DefaultConfig            // ReadTimeout: Duration(15 * time.Second)
configFromFlags := ServerConfig{ /* ... */ ReadTimeout: Duration(a.readTimeout) }
mergo.Merge(&config, configFromFlags, mergo.WithOverride)

mergo.Merge with WithOverride does not override a destination field when the source field is a zero value. An explicit -read_timeout 0 parses to a.readTimeout == 0, which is indistinguishable from the flag being unset, so mergo skips it and the 15s DefaultConfig.ReadTimeout stands. Only a non-zero (negative) duration overrides.

Proposed fix

Distinguish "flag not provided" from "explicitly set" for the timeout flags — e.g. re-apply them after the merge via flag.Visit — so -read_timeout 0 maps to ReadTimeout: 0 (no timeout) as documented. This mirrors the existing IsSet() handling used for the bool flags. PR to follow.

Workaround

-read_timeout=-1s (any negative duration).