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# decapitated
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Headless ‘Chrome’ Orchestration
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## Description
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The ‘Chrome’ browser <https://www.google.com/chrome/> has a headless
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mode which can be instrumented programmatically. Tools are provided to
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perform headless ‘Chrome’ instrumentation on the command-line, including
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retrieving the javascript-executed web page, PDF output or screen shot
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of a URL.
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## IMPORTANT
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You'll need to set an envrionment variable `HEADLESS_CHROME` to use this package.
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If this value is not set, a location heuristic is used on package start which looks
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for the following depending on the operating system:
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- Windows(32bit): `C:/Program Files/Google/Chrome/Application/chrome.exe`
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- Windows(64bit): `C:/Program Files (x86)/Google/Chrome/Application/chrome.exe`
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- macOS: `/Applications/Google\ Chrome.app/Contents/MacOS/Google\ Chrome`
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- Linux: `/usr/bin/google-chrome`
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If a verification test fails, you will be notified.
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**It is HIGHLY recommended** that you use `decapitated::download_chromium()` to use
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a standalone version of Chrome with this packge for your platform.
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It's best to use `~/.Renviron` to store this value.
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## Working around headless Chrome & OS security restrictions:
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Security restrictions on various operating systems and OS configurations
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can cause headless Chrome execution to fail. As a result, headless
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Chrome operations should use a special directory for `decapitated`
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package operations. You can pass this in as `work_dir`. If `work_dir` is
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`NULL` a `.rdecapdata` directory will be created in your home directory
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and used for the data, crash dumps and utility directories for Chrome
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operations.
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`tempdir()` does not always meet these requirements (after testing on
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various macOS 10.13 systems) as Chrome does some interesting attribute
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setting for some of its file operations.
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If you pass in a `work_dir`, it must be one that does not violate OS
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security restrictions or headless Chrome will not function.
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## Helping it “always work”
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The three core functions have a `prime` parameter. In testing (again,
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especially on macOS), I noticed that the first one or two requests to a
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URL often resulted in an empty `<body>` response. I don’t use Chrome as
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my primary browser anymore so I’m not sure if that has something to do
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with it, but requests after the first one or two do return content. The
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`prime` parameter lets you specify `TRUE`, `FALSE` or a numeric value
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that will issue the URL retrieval multiple times before returning a
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result (or generating a PDF or PNG). Until there is more granular
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control over the command-line execution of headless Chrome.
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## What’s in the tin?
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The following functions are implemented:
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- `downlaod_chromium`: Download a standalone version of Chromium (recommended)
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- `chrome_dump_pdf`: “Print” to PDF
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- `chrome_read_html`: Read a URL via headless Chrome and return the
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raw or rendered ’
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<body>
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‘’innerHTML’ DOM elements
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- `chrome_shot`: Capture a screenshot
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- `chrome_version`: Get Chrome version
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- `get_chrome_env`: get an envrionment variable ‘HEADLESS\_CHROME’
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- `set_chrome_env`: set an envrionment variable ‘HEADLESS\_CHROME’
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## Installation
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``` r
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devtools::install_github("hrbrmstr/decapitated")
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```
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## Usage
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``` r
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library(decapitated)
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# current verison
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packageVersion("decapitated")
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```
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## [1] '0.3.0'
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``` r
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chrome_version()
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chrome_read_html("http://httpbin.org/")
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```
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## {xml_document}
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## <html>
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## [1] <head>\n<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">\n<meta http-equiv="content-type" valu ...
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## [2] <body id="manpage">\n<a href="http://github.com/kennethreitz/httpbin"><img style="position: absolute; top: 0; rig ...
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``` r
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chrome_dump_pdf("http://httpbin.org/")
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```
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``` r
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chrome_shot("http://httpbin.org/")
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## format width height colorspace filesize
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## 1 PNG 1600 1200 sRGB 215680
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```
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