Add PDF to fax conversion support

- pdf.rs: Ghostscript-based PDF to TIFF-F conversion
- tiff_to_fax_document: Parse TIFF and convert to 1-bit fax format
- CLI: Add 'convert' subcommand for dry testing
- CLI: Add resolution option for send command
- Test files for PDF/TIFF conversion validation

test/test_conversion.py

@@ -0,0 +1,76 @@
+#!/usr/bin/env python3
+import subprocess
+import os
+
+# Test PDF to TIFF-F conversion
+pdf_path = "/Users/accusys/telfax/test/testfax.pdf"
+tiff_path = "/Users/accusys/telfax/test/testfax_converted.tif"
+
+print("=== Testing PDF → TIFF-F Conversion ===")
+
+# Run ghostscript
+result = subprocess.run([
+    "gs", "-dBATCH", "-dNOPAUSE", "-q",
+    "-sDEVICE=tiffg3",
+    "-r204x196",  # Fine resolution
+    "-sOutputFile", tiff_path,
+    pdf_path
+], capture_output=True, text=True)
+
+if result.returncode != 0:
+    print(f"Ghostscript failed: {result.stderr}")
+    exit(1)
+
+# Check output
+if os.path.exists(tiff_path):
+    size = os.path.getsize(tiff_path)
+    print(f"✓ TIFF-F created: {tiff_path}")
+    print(f"  Size: {size} bytes")
+    
+    # Get TIFF info
+    import struct
+    
+    with open(tiff_path, 'rb') as f:
+        header = f.read(8)
+        if header[:2] == b'II':
+            print("  Byte order: Little-endian")
+        elif header[:2] == b'MM':
+            print("  Byte order: Big-endian")
+        
+        # Read IFD offset
+        if header[:2] == b'II':
+            ifd_offset = struct.unpack('<I', header[4:8])[0]
+        else:
+            ifd_offset = struct.unpack('>I', header[4:8])[0]
+        
+        f.seek(ifd_offset)
+        num_entries = struct.unpack('<H' if header[:2] == b'II' else '>H', f.read(2))[0]
+        print(f"  IFD entries: {num_entries}")
+        
+        # Read key tags
+        for i in range(num_entries):
+            tag = struct.unpack('<H' if header[:2] == b'II' else '>H', f.read(2))[0]
+            type_ = struct.unpack('<H' if header[:2] == b'II' else '>H', f.read(2))[0]
+            count = struct.unpack('<I' if header[:2] == b'II' else '>I', f.read(4))[0]
+            value_offset = f.read(4)
+            
+            # Tags of interest: 256=width, 257=height, 259=compression, 262=photometric
+            if tag == 256:  # Width
+                val = struct.unpack('<I' if header[:2] == b'II' else '>I', value_offset)[0]
+                print(f"  Width: {val} pixels")
+            elif tag == 257:  # Height
+                val = struct.unpack('<I' if header[:2] == b'II' else '>I', value_offset)[0]
+                print(f"  Height: {val} lines")
+            elif tag == 259:  # Compression
+                val = struct.unpack('<H' if header[:2] == b'II' else '>H', value_offset[:2])[0]
+                comp_names = {1: "None", 3: "Group 3 MH", 4: "Group 4 MMR"}
+                print(f"  Compression: {comp_names.get(val, val)}")
+            elif tag == 262:  # PhotometricInterpretation
+                val = struct.unpack('<H' if header[:2] == b'II' else '>H', value_offset[:2])[0]
+                photo_names = {0: "WhiteIsZero", 1: "BlackIsZero"}
+                print(f"  Photometric: {photo_names.get(val, val)}")
+else:
+    print("✗ TIFF-F not created")
+    exit(1)
+
+print("\n=== Conversion Test Passed ===")

test/test_tiff_convert.rs

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+use telfax::document::pdf::{pdf_to_fax_document, tiff_to_fax_document};
+use telfax::config::FaxResolution;
+use std::path::Path;
+
+fn main() {
+    let tiff_path = "/Users/accusys/telfax/test/testfax.tif";
+    let tiff_data = std::fs::read(tiff_path).expect("Failed to read TIFF");
+
+    println!("=== Testing TIFF → FaxDocument conversion ===");
+    println!("Input TIFF: {} bytes", tiff_data.len());
+
+    let doc = tiff_to_fax_document(&tiff_data).expect("Conversion failed");
+
+    println!("Converted successfully:");
+    println!("  Pages: {}", doc.pages.len());
+    for (i, page) in doc.pages.iter().enumerate() {
+        println!("  Page {}: {}x{} pixels, {} bytes",
+            i + 1, page.width_pels, page.rows, page.pixels.len());
+    }
+
+    // Verify pixel data - check some sample values
+    let page = &doc.pages[0];
+    let bytes_per_row = ((page.width_pels + 7) / 8) as usize;
+    
+    println!("  Bytes per row: {}", bytes_per_row);
+    println!("  Expected rows: {}", page.rows);
+    println!("  Actual data rows: {}", page.pixels.len() / bytes_per_row);
+
+    // Sample first few bytes of first row
+    println!("  First row bytes (hex): {:02x?}", &page.pixels[0..8.min(bytes_per_row)]);
+    
+    println!("\n=== Test Passed ===");
+}

test/testfax.ps

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+%!PS-Adobe-3.0
+%%Pages: 1
+%%PageOrder: Ascend
+%%BoundingBox: 0 0 612 792
+%%EndComments
+
+%%BeginProlog
+/Dict 2 dict def
+Dict begin
+/PageSize [612 792] def
+end
+
+%%EndProlog
+
+%%Page: 1 1
+10 750 moveto
+/Fnt1 12/Times-Roman findfont definefont pop
+/Fnt1 12 selectfont
+(Telfax Test Document - Page 1) show
+
+10 730 moveto
+(This is a test fax transmission from telfax Rust server.) show
+
+10 700 moveto
+(Testing US Robotics 56K FAX USB Modem) show
+
+10 680 moveto
+(Date: 2026-07-01) show
+
+10 600 moveto
+/BoxTimes-Roman 14 selectfont
+(TEST FAX CONTENT) show
+
+10 550 moveto
+(This document tests the Class 1 fax protocol implementation.) show
+
+showpage
+%%PageTrailer
+
+%%Trailer
+%%EOF