fix(gmail): use case-insensitive matching for email headers in parse_message_headers by gura105 · Pull Request #643 · googleworkspace/cli

gura105 · 2026-03-30T10:12:17Z

Description

parse_message_headers uses exact case-sensitive string matching for header names ("Cc", "From", etc.), but the Gmail API preserves original header casing from the sending MTA. Per RFC 5322 §1.2.2, header field names are case-insensitive.

This causes +reply-all (and other commands) to silently drop CC recipients when the original message was sent through an MTA that uses non-canonical casing (e.g., Microsoft Exchange emits "CC" instead of "Cc").

Root cause

// Before: exact match — "CC" falls through to _ => {}
match name {
    "Cc" => append_address_list_header_value(&mut parsed.cc, value),
    ...
}

Fix

Use eq_ignore_ascii_case match guards for zero-allocation case-insensitive matching, consistent with the existing get_part_header and extract_header functions in the same file.

// After: case-insensitive — "CC", "Cc", "cc" all match
match name {
    s if s.eq_ignore_ascii_case("cc") => {
        append_address_list_header_value(&mut parsed.cc, value)
    }
    ...
}

This also simplifies the Message-ID arm from "Message-ID" | "Message-Id" to just eq_ignore_ascii_case("message-id").

Scope

All headers in the match block are affected, not just Cc:

Header	Impact if missed
`From`	Hard error (`"Message is missing From header"`)
`Message-ID`	Hard error (`"Message is missing Message-ID header"`)
`To`	`+reply-all` misses To recipients
`CC`	`+reply-all` drops CC recipients
`Reply-To`	Reply goes to wrong recipient
`References`	Threading breaks

Tests

3 new tests (701 total, up from 698):

test_parse_message_headers_all_uppercase — all-caps headers (Exchange/Outlook pattern)
test_parse_message_headers_all_lowercase — all-lowercase headers
test_parse_message_headers_mixed_case — canonical + non-canonical mix

All existing tests pass unchanged.

Fixes #642

Checklist:

My code follows the AGENTS.md guidelines (no generated google-* crates).
I have run cargo fmt --all to format the code perfectly.
I have run cargo clippy -- -D warnings and resolved all warnings.
I have added tests that prove my fix is effective or that my feature works.
I have provided a Changeset file (e.g. via pnpx changeset) to document my changes.

…message_headers The Gmail API preserves original header casing from the sending MTA. For example, Microsoft Exchange emits "CC" instead of "Cc". Per RFC 5322 §1.2.2, header field names are case-insensitive. parse_message_headers used exact case-sensitive string matching, so headers like "CC", "FROM", or "message-id" silently fell through to the catch-all, dropping recipients and metadata. This change normalizes header names via to_ascii_lowercase() before matching, consistent with the existing get_part_header function in the same file which already uses eq_ignore_ascii_case. Fixes googleworkspace#642

changeset-bot · 2026-03-30T10:12:23Z

🦋 Changeset detected

Latest commit: 1656739

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

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@googleworkspace/cli	Patch

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google-cla · 2026-03-30T10:12:28Z

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gemini-code-assist · 2026-03-30T10:12:28Z

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses an issue where email header parsing was failing due to strict case-sensitive matching. By normalizing header names to lowercase, the system now correctly handles headers regardless of how they are formatted by the sending mail transfer agent, ensuring that essential metadata is correctly extracted and preserved.

Highlights

Case-Insensitive Header Matching: Updated parse_message_headers to normalize email header names to lowercase before matching, ensuring compatibility with non-canonical header casing from various MTAs.
Improved Robustness: Prevents silent data loss for CC recipients and other critical headers when messages are processed through systems like Microsoft Exchange.
Expanded Test Coverage: Added three new test cases covering all-uppercase, all-lowercase, and mixed-case header scenarios to verify the fix.

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gemini-code-assist

Code Review

This pull request implements case-insensitive matching for Gmail email headers in parse_message_headers to comply with RFC 5322. It includes a changeset and comprehensive unit tests for various casing scenarios. A performance improvement was suggested to use eq_ignore_ascii_case with match guards instead of to_ascii_lowercase() to avoid unnecessary string allocations within the loop.

gemini-code-assist · 2026-03-30T10:13:49Z

crates/google-workspace-cli/src/helpers/gmail/mod.rs

+        match name.to_ascii_lowercase().as_str() {
+            "from" => parsed.from = value.to_string(),
+            "reply-to" => append_address_list_header_value(&mut parsed.reply_to, value),
+            "to" => append_address_list_header_value(&mut parsed.to, value),
+            "cc" => append_address_list_header_value(&mut parsed.cc, value),
+            "subject" => parsed.subject = value.to_string(),
+            "date" => parsed.date = value.to_string(),
+            "message-id" => parsed.message_id = value.to_string(),
+            "references" => append_header_value(&mut parsed.references, value),
            _ => {}
        }


While this correctly implements case-insensitive matching, calling to_ascii_lowercase() inside the loop creates a new String allocation for every header. This can be inefficient, especially for messages with many headers.

For better performance and consistency with other functions in this file (like get_part_header), you can use eq_ignore_ascii_case with match guards. This performs a case-insensitive comparison without any heap allocations.

Suggested change

match name.to_ascii_lowercase().as_str() {

"from" => parsed.from = value.to_string(),

"reply-to" => append_address_list_header_value(&mut parsed.reply_to, value),

"to" => append_address_list_header_value(&mut parsed.to, value),

"cc" => append_address_list_header_value(&mut parsed.cc, value),

"subject" => parsed.subject = value.to_string(),

"date" => parsed.date = value.to_string(),

"message-id" => parsed.message_id = value.to_string(),

"references" => append_header_value(&mut parsed.references, value),

_ => {}

}

match name {

s if s.eq_ignore_ascii_case("from") => parsed.from = value.to_string(),

s if s.eq_ignore_ascii_case("reply-to") => append_address_list_header_value(&mut parsed.reply_to, value),

s if s.eq_ignore_ascii_case("to") => append_address_list_header_value(&mut parsed.to, value),

s if s.eq_ignore_ascii_case("cc") => append_address_list_header_value(&mut parsed.cc, value),

s if s.eq_ignore_ascii_case("subject") => parsed.subject = value.to_string(),

s if s.eq_ignore_ascii_case("date") => parsed.date = value.to_string(),

s if s.eq_ignore_ascii_case("message-id") => parsed.message_id = value.to_string(),

s if s.eq_ignore_ascii_case("references") => append_header_value(&mut parsed.references, value),

_ => {}

}

googleworkspace-bot · 2026-03-30T10:21:07Z

/gemini review

gemini-code-assist

Code Review

This pull request updates the Gmail parse_message_headers function to perform case-insensitive matching of email header names by converting them to lowercase, ensuring compliance with RFC 5322. It also adds unit tests to verify correct parsing of uppercase, lowercase, and mixed-case headers. I have no feedback to provide.

Avoids per-header String allocation in the loop. Consistent with get_part_header in the same file. Addresses gemini-code-assist review feedback.

googleworkspace-bot · 2026-03-30T10:23:57Z

/gemini review

gemini-code-assist

Code Review

This pull request updates the parse_message_headers function in the Gmail helper module to implement case-insensitive matching for email headers, ensuring compliance with RFC 5322. The implementation replaces static string matching with match guards using eq_ignore_ascii_case. New unit tests have been added to validate the handling of uppercase, lowercase, and mixed-case header names. I have no feedback to provide as the changes correctly address the issue and include appropriate test coverage.

googleworkspace-bot added the area: core Core CLI parsing, commands, error handling, utilities label Mar 30, 2026

gemini-code-assist bot reviewed Mar 30, 2026

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chore: retrigger CLA check

6f89e36

gemini-code-assist bot reviewed Mar 30, 2026

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refactor: use eq_ignore_ascii_case instead of to_ascii_lowercase

1656739

Avoids per-header String allocation in the loop. Consistent with get_part_header in the same file. Addresses gemini-code-assist review feedback.

gemini-code-assist bot reviewed Mar 30, 2026

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fix(gmail): use case-insensitive matching for email headers in parse_message_headers#643

fix(gmail): use case-insensitive matching for email headers in parse_message_headers#643
gura105 wants to merge 3 commits intogoogleworkspace:mainfrom
gura105:fix/header-case-insensitive

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