Does IPATool Support Resuming Interrupted IPA Downloads? Complete Technical Guide

Yes, IPATool supports resuming interrupted IPA downloads by detecting partial files and utilizing HTTP Range requests to fetch only the remaining bytes, appending new data to existing files without restarting the entire transfer.

IPATool, the command-line utility for downloading iOS app packages from the App Store, implements robust download-resume functionality at the HTTP-client layer. According to the majd/ipatool source code, this feature works transparently when you re-run the same download command, automatically continuing where the previous attempt left off.

How IPATool Implements Download Resume

The resume mechanism operates by inspecting the local filesystem for partially downloaded files before initiating HTTP requests. When IPATool detects an existing file at the destination path, it calculates the current file size and requests only the missing data from the server.

The Core Logic in appstore_download.go

The primary implementation resides in pkg/appstore/appstore_download.go (lines 21–23). The code first checks for an existing partial file using the operating system’s Stat function:

stat, err := t.os.Stat(dst)

If the file exists, IPATool constructs an HTTP Range header that specifies the starting byte position as the current file size. This instructs the App Store server to stream only the remaining portion of the IPA file:

req.Header.Add("range", fmt.Sprintf("bytes=%d-", stat.Size()))

The client then opens the existing file in append mode and writes the incoming data, preserving previously downloaded content.

CLI Integration in cmd/download.go

The high-level cmd/download.go file invokes this underlying routine, meaning any download initiated via the command line automatically benefits from resume support. You do not need to specify special flags; the tool detects the partial file and applies the Range header logic automatically.

Practical Usage Examples

Resuming a Download from the Command Line

If a network failure or user cancellation interrupts your download, simply re-execute the original command. IPATool will detect the partial myapp.ipa file and continue the transfer:

# First attempt (interrupted by network issue)

ipatool download -i 123456789 -o myapp.ipa

# Re-run identical command to resume from existing file

ipatool download -i 123456789 -o myapp.ipa

The second invocation checks the file size of myapp.ipa, sends the appropriate bytes= Range header, and appends only the missing data.

Examining the Resume Implementation

The following simplified excerpt from pkg/appstore/appstore_download.go illustrates how IPATool prepares the resume request:

stat, err := t.os.Stat(dst)               // Check existing file size
if err != nil { 
    return fmt.Errorf("failed to stat file: %w", err) 
}

if req != nil && stat != nil {
    // Request only the missing bytes from current position to end
    req.Header.Add("range", fmt.Sprintf("bytes=%d-", stat.Size()))
}

This logic ensures that interrupted downloads can continue efficiently without redundant data transfer.

Key Source Files

• pkg/appstore/appstore_download.go – Contains the core download implementation, including the os.Stat check and HTTP Range header injection (lines 21–23).

• cmd/download.go – Implements the CLI download command that wraps the appstore download routine, providing automatic resume support to end users.

• pkg/http/client.go – Provides the HTTP client used to execute requests with the custom Range headers and handle the server response stream.

Summary

• IPATool supports resuming interrupted IPA downloads transparently through HTTP Range requests.
• The resume logic checks for partial files using os.Stat and requests remaining bytes starting from the current file size.
• Re-running the same ipatool download command automatically continues incomplete downloads without requiring special flags.
• The implementation is contained primarily in pkg/appstore/appstore_download.go and utilized by cmd/download.go.

Frequently Asked Questions

How does IPATool detect partial downloads to resume?

IPATool uses the operating system’s Stat function to check if a file already exists at the destination path (t.os.Stat(dst)). If present, it calculates the file size and includes this value in an HTTP Range header to request only the remaining bytes.

Which command should I use to resume an interrupted IPA download?

Use the standard download command. According to cmd/download.go, simply re-running the identical command (same -i and -o arguments) will automatically detect the partial file and resume the transfer using the Range header logic.

Where is the resume logic located in the IPATool source code?

The resume implementation is located in pkg/appstore/appstore_download.go, specifically where the code checks for existing files and constructs the Range header (lines 21–23). The HTTP client handling resides in pkg/http/client.go.

Does resuming an IPA download require special command-line flags?

No special flags are required. The resume functionality is automatic and transparent. When IPATool detects an existing partial file at the specified output path, it automatically applies the HTTP Range request without user intervention.

{
  "mcpServers": {
    "instagit": {
      "command": "npx",
      "args": ["-y", "instagit@latest"]
    }
  }
}