Refactor fetch_key_file to include retry logic and improve error handling (#9)

* Refactor fetch_key_file to include retry logic and improve error handling

* Enhance fetch_key_file with retry logic and update documentation to reflect changes

* Bump script version to 0.0.8

Author: locus313

.github/copilot-instructions.md

@@ -13,7 +13,7 @@ This document provides comprehensive guidance for AI coding agents and contribut
   - Support for multiple fetch methods (`raw`, `api`, `ghuser`).
   - Logging and error handling.
   - Configuration loading from `users.conf`.
-  - A helper function `fetch_key_file` to handle key retrieval logic.
+  - A helper function `fetch_key_file` to handle key retrieval logic with retries for failed operations.
 
 ### Configuration
 - **`users.conf`**: Defines users and their key sources. Example structure:
@@ -97,3 +97,8 @@ This document provides comprehensive guidance for AI coding agents and contribut
 - **`raw`**: Fetches keys from a public URL.
 - **`api`**: Fetches keys from a private GitHub repository using the GitHub API.
 - **`ghuser`**: Fetches public keys from a GitHub user's profile.
+
+### Enhanced Error Handling
+- The `fetch_key_file` function includes a retry mechanism for failed fetch operations.
+- By default, it retries up to 3 times with a 2-second delay between attempts.
+- Logs detailed error messages for each failed attempt and skips the user if all retries fail.

README.md

@@ -12,6 +12,7 @@ This Bash script pulls `authorized_keys` files from remote URLs and updates SSH
   - ✅ GitHub user public keys (method: `ghuser`)
 - Safe: Only updates keys if they’ve changed
 - Logs activity per user
+- Retries failed fetch operations up to 3 times with a delay
 
 ## ⚙️ Configuration
 
@@ -41,10 +42,11 @@ declare -A USER_KEYS=(
 ## Usage
 
 1. Edit the `users.conf` file to define users and their key URLs or GitHub usernames.
-2. If using the `api` method, either export your GitHub token or set `CONF_GITHUB_TOKEN` in `users.conf`:
+2. If using the `api` method, either export your GitHub token:
    ```bash
    export GITHUB_TOKEN=your_token_here
    ```
+   or set `CONF_GITHUB_TOKEN` in `users.conf`.
 3. Make sure the script is executable:
    ```bash
    chmod +x sync-ssh-keys.sh
@@ -58,5 +60,18 @@ declare -A USER_KEYS=(
 
 - The script sources `users.conf` for configuration.
 - Uses a helper function `fetch_key_file` to fetch keys using the appropriate method.
+- Includes a retry mechanism for failed fetch operations (3 attempts with a 2-second delay).
 - Only updates a user's `authorized_keys` if the remote file has changed.
 - Logs all actions with timestamps.
+
+## Examples
+
+### Adding a New User
+1. Add the user to `users.conf`:
+   ```bash
+   ["newuser"]="ghuser:newuser-github-username"
+   ```
+2. Run the script to sync keys:
+   ```bash
+   ./sync-ssh-keys.sh
+   ```

sync-ssh-keys.sh

@@ -2,7 +2,7 @@
 set -euo pipefail
 
 # shellcheck disable=SC2034  # planned to be used in a future release
-SCRIPT_VERSION="0.0.7"
+SCRIPT_VERSION="0.0.8"
 
 # === Load user configuration ===
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
@@ -30,24 +30,30 @@ fetch_key_file() {
   local METHOD="$1"
   local TARGET="$2"
   local OUTFILE="$3"
+  local RETRIES=3
+  local RETRY_DELAY=2
 
-  if [[ "$METHOD" == "raw" ]]; then
-    curl -fsSL "$TARGET" -o "$OUTFILE"
-    return $?
-  elif [[ "$METHOD" == "api" ]]; then
-    : "${GITHUB_TOKEN:?GITHUB_TOKEN is required for API access}"
-    curl -fsSL -H "Authorization: token $GITHUB_TOKEN" \
-               -H "Accept: application/vnd.github.v3.raw" \
-               "$TARGET" -o "$OUTFILE"
-    return $?
-  elif [[ "$METHOD" == "ghuser" ]]; then
-    # TARGET is the GitHub username
-    curl -fsSL "https://github.com/${TARGET}.keys" -o "$OUTFILE"
-    return $?
-  else
-    log_message "Error: Unsupported method '$METHOD' encountered for URL '$TARGET'. Halting execution."
-    exit 2
-  fi
+  for ((i=1; i<=RETRIES; i++)); do
+    if [[ "$METHOD" == "raw" ]]; then
+      curl -fsSL "$TARGET" -o "$OUTFILE" && return 0
+    elif [[ "$METHOD" == "api" ]]; then
+      : "${GITHUB_TOKEN:?GITHUB_TOKEN is required for API access}"
+      curl -fsSL -H "Authorization: token $GITHUB_TOKEN" \
+                 -H "Accept: application/vnd.github.v3.raw" \
+                 "$TARGET" -o "$OUTFILE" && return 0
+    elif [[ "$METHOD" == "ghuser" ]]; then
+      curl -fsSL "https://github.com/${TARGET}.keys" -o "$OUTFILE" && return 0
+    else
+      log_message "Error: Unsupported method '$METHOD' encountered for URL '$TARGET'. Halting execution."
+      exit 2
+    fi
+
+    log_message "Attempt $i/$RETRIES failed for method '$METHOD' and URL '$TARGET'. Retrying in $RETRY_DELAY seconds..."
+    sleep "$RETRY_DELAY"
+  done
+
+  log_message "Error: All $RETRIES attempts failed for method '$METHOD' and URL '$TARGET'. Skipping."
+  return 1
 }
 
 TMP_FILES=()
@@ -58,16 +64,19 @@ for USER in "${!USER_KEYS[@]}"; do
   ENTRY="${USER_KEYS[$USER]}"
   METHOD="${ENTRY%%:*}"
   URL="${ENTRY#*:}"
+
   # Ensure user exists
   if ! id "$USER" &>/dev/null; then
     log_message "User '$USER' does not exist. Skipping."
     continue
   fi
+
   USER_HOME=$(getent passwd "$USER" | cut -d: -f6)
   if [ -z "$USER_HOME" ]; then
     log_message "Failed to determine home directory for user '$USER'. Skipping."
     continue
   fi
+
   AUTH_KEYS="$USER_HOME/.ssh/authorized_keys"
   SSH_DIR="$(dirname "$AUTH_KEYS")"
 
@@ -76,21 +85,26 @@ for USER in "${!USER_KEYS[@]}"; do
     mkdir -p "$SSH_DIR"
     chown "$USER:$USER" "$SSH_DIR"
     chmod 700 "$SSH_DIR"
-    log_message "Created .ssh directory for user '$USER'"
+    log_message "Created .ssh directory for user '$USER' at $SSH_DIR."
   fi
 
   log_message "Fetching key file for $USER from $URL (method: $METHOD)"
   if ! fetch_key_file "$METHOD" "$URL" "$TMP_FILE"; then
-    log_message "Failed to fetch key file for user '$USER' from $URL. Skipping."
+    log_message "Failed to fetch key file for user '$USER' from $URL after multiple attempts. Skipping."
     continue
   fi
 
-  if [ ! -f "$AUTH_KEYS" ] || ! cmp -s "$TMP_FILE" "$AUTH_KEYS"; then
-    cp "$TMP_FILE" "$AUTH_KEYS"
-    chown "$USER:$USER" "$AUTH_KEYS"
-    chmod 600 "$AUTH_KEYS"
-    log_message "Updated authorized_keys for user '$USER'"
+  if [ ! -f "$AUTH_KEYS" ]; then
+    log_message "No existing authorized_keys file for user '$USER'. Creating a new one."
+  elif ! cmp -s "$TMP_FILE" "$AUTH_KEYS"; then
+    log_message "Changes detected in authorized_keys for user '$USER'. Updating the file."
   else
-    log_message "No changes for user '$USER'"
+    log_message "No changes detected in authorized_keys for user '$USER'."
+    continue
   fi
+
+  cp "$TMP_FILE" "$AUTH_KEYS"
+  chown "$USER:$USER" "$AUTH_KEYS"
+  chmod 600 "$AUTH_KEYS"
+  log_message "Updated authorized_keys for user '$USER' at $AUTH_KEYS."
 done