When configuring Nginx to serve static files with gzip compression enabled, you might notice the Content-Length header is missing from responses. This happens particularly when using the alias directive in Nginx configurations.

The Content-Length header is crucial for:

• Progress tracking in client applications
• Connection reuse optimization
• Accurate download size reporting
• Better HTTP/1.1 compatibility

Here's how to force Nginx to include Content-Length even with gzip:

server {
    listen 80;
    server_name example.com;

    gzip on;
    gzip_types text/plain text/css application/json;

    location /static/ {
        alias /path/to/static/files/;
        
        # The key directives:
        gzip_static on;
        gzip_vary on;
        gzip_proxied any;
        
        # Force Content-Length
        add_header Content-Length "";
        if ($http_accept_encoding ~ gzip) {
            add_header Content-Length $upstream_http_content_length;
        }
    }
}

If the above doesn't work, try these variations:

# Option 1: Pre-compressed files
location /static/ {
    alias /path/to/files/;
    gzip_static on;
}

# Option 2: Disable gzip for certain files
location ~* \.(jpg|png|gif|ico|pdf|flv)$ {
    gzip off;
    alias /path/to/files/;
}

# Option 3: Use root instead of alias
location /static/ {
    root /path/to;
    gzip on;
    gzip_types *;
}

Verify the headers with curl:

curl -I -H "Accept-Encoding: gzip" http://yourserver/static/file.txt

Look for both Content-Encoding: gzip and Content-Length in the response headers.

When working with Nginx's gzip compression for static files, you might notice the absence of the Content-Length header in responses. This behavior occurs because Nginx doesn't know the compressed size until after compression is complete, and by default, it opts for chunked transfer encoding instead.

The Content-Length header is crucial for:

• Accurate progress tracking for clients
• Better cache control mechanisms
• Improved download resume capabilities
• Proper connection management

The most efficient approach is to use pre-compressed files with the gzip_static module:

location /static/ {
    gzip_static on;
    alias /path/to/your/files/;
    add_header Content-Length $content_length;
}

If you must compress on-the-fly, you can use this workaround:

location /compressed/ {
    gzip on;
    gzip_types *;
    
    # Store compressed output in memory
    gzip_buffers 16 8k;
    gzip_buffer_size 32k;
    
    # Calculate after compression
    header_filter_by_lua '
        ngx.header["Content-Length"] = #ngx.arg[1]
    ';
}

Be aware that forcing Content-Length for dynamic compression comes with trade-offs:

• Memory usage increases as Nginx must buffer the entire compressed output
• Latency may increase for large files
• CPU overhead grows with compression and size calculation

Verify your setup with curl:

curl -I -H "Accept-Encoding: gzip" http://yourserver.com/static/file.txt

Look for both Content-Encoding: gzip and Content-Length headers in the response.