Operation Flows and Hooks

This article introduces the important flows in Paperlib, as well as the hooks available in these operation flows.

Introduction to Hooks

In Paperlib, we have placed hooks with different names in different places. A hook extension can register to the corresponding hook point to intervene in the operation flow of Paperlib. There are two types of hook points.

Modify Hook Points

• Purpose: This type of hook point is used to modify the arguments passed by the hook point, or the variables within the argument objects, but cannot change the type, and finally returns the modified arguments.

• Type of Callback Return Value: Modify Hook requires the return value of the callback function to be an array, each element of which corresponds to the input argument array. For example, if the arguments passed by the hook point are (arg1: string, arg2: {value: number}), you can modify arg1 to another string and arg2.value to another number in the callback function of the hook, but you cannot change the type of arg1 to a number, or change the type of arg2 to another type. The return value of the callback function must be an array composed of modified arguments: [arg1, arg2]. Note that even if only one argument is passed in, an array with one element needs to be returned. Because the input arguments are always treated as an arguments array

Transform Hook Points

• Purpose: This type of hook point can modify the data flow in the operation process of Paperlib. It is used to transform the input arguments into other forms of data and then return.
• Callback Return Value Type: It can be other types, but usually different hook points have expected return value types. For example, the scrapeEntry hook point expects the return value type to be an array of PaperEntity.

For information on how to register hooks and how to write hook extensions, please refer to Hook extensions.

Paper Import Process

Whether it is imported by dragging files or imported from browser extensions, after forming the corresponding source payload, it will enter the paper import process. The diagram of the paper import process is as follows:

In this process, the main hook points are in the scrapeEntry() and scrapeMetadata() methods of ScrapeService.

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scrapeEntry()

The main task of scrapeEntry() is to convert these data from different types of sources into the internal data structure PaperEntity of Paperlib, and fill in the important fields of PaperEntity as much as possible (such as: title, doi, arxivID, etc.) for the subsequent scrapeMetadata() method to search and complete its paper metadata.

After receiving the import of the paper source, we first call scrapeEntry(). Its main argument is an array of SourcePayload, that is, the data of the paper source. source payload contains the type field indicating the type of source, and the data of the source:

interface SourcePayload {
  type: "file" | "webcontent";
  // For file type, value is the path of the file
  // For webcontent type, value is WebContentSourcePayload
  value: string | WebContentSourcePayload;
}

interface WebContentSourcePayload {
  url: string;             // Source page's url
  document: string;        // Source page's html              
  cookies?: string;        // Some pages may contain cookies
}

The return type of scrapeEntry() is an array of PaperEntity, because even if the SourcePayload array only contains one source payload, it may contain multiple papers. For example, when importing by dragging files, the dragged file might be a BibTex file, which contains information about multiple papers.

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scrapeMetadata()

The return value of scrapeEntry() will be passed into the scrapeMetadata() method. The main task of scrapeMetadata() is to search for the paper's metadata from various databases on the internet and complete all fields in PaperEntity. The return type of scrapeMetadata() is also an array of PaperEntity.

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As shown in the diagram, there are six hook points in this operation flow, five of the Modify type and one of the Transform type.

beforeScrapeEntry

Parameter	Value
Type	Modify
Location	At the very beginning of the scrapeEntry() method, before the SourcePayload being converted to PaperEntity
Callback arguments	SourcePayload[]
Callback Return Value	ArgumentArray<SourcePayload[]>

scrapeEntry

Parameter	Value
Type	Transform
Location	The main hook point of scrapeEntry(), accepts SourcePayload 数组 and outputs PaperEntity 数组
Callback arguments	SourcePayload[]
Callback Return Value	PaperEntity[]

afterScrapeEntry

Parameter	Value
Type	Modify
Location	At the end of the scrapeEntry() method, after the SourcePayload being converted to PaperEntity
Callback arguments	PaperEntity[]
Callback Return Value	ArgumentArray<PaperEntity[]>

beforeScrapeMetadata

Parameter	Value
Type	Modify
Location	At the very beginning of the scrapeMetadata() method, before searching for metadata
Callback arguments	paperEntities: PaperEntity[], scrapers: string[], force: boolean
Callback Return Value	ArgumentArray<paperEntities: PaperEntity[], scrapers: string[], force: boolean>

Here, scrapers is an array of strings. If it is not empty, it means that the user has chosen to search with specific scrapers. force indicates whether to force the search. If true, it will ignore the existing metadata in PaperEntity and force the search.

scrapeMetadata

Parameter	Value
Type	Modify
Location	The main hook point of scrapeMetadata(), accepts an array of PaperEntity, can modify each property and return
Callback arguments	paperEntities: PaperEntity[], scrapers: string[], force: boolean
Callback Return Value	ArgumentArray<paperEntities: PaperEntity[], scrapers: string[], force: boolean>

afterScrapeMetadata

Parameter	Value
Type	Modify
Location	At the end of the scrapeMetadata() method, after searching for metadata
Callback arguments	paperEntities: PaperEntity[], scrapers: string[], force: boolean
Callback Return Value	ArgumentArray<paperEntities: PaperEntity[], scrapers: string[], force: boolean>

Paper PDF Locating

When a paper does not have a corresponding PDF file, Paperlib will display a button in the detail panel to locate for available PDFs on the internet and download them. After clicking this button, it will enter the paper PDF locating process. The main function of the paper PDF locating process is the locateFileOnWeb() method of FileService. There is one available hook in this process.

locateFile

Parameter	Value
Type	Modify
Location	Inside the locateFileOnWeb() method
Callback arguments	PaperEntity[]
Callback Return Value	ArgumentArray<PaperEntity[]>

Reference Exporting Process

In general, when exporting references, we need to get the array of PaperEntity to be exported, and then convert it into a citation.js's Cite object. Finally, we convert the Cite object into a string of the corresponding format, such as a BibTex string. For details, please refer to the various functions of ReferenceService in the GitHub code.

beforeExportBibItem

Parameter	Value
Type	Modify
Location	At the very beginning of the exportBibItem() method
Callback arguments	PaperEntity[]
Callback Return Value	ArgumentArray<PaperEntity[]>

citeObjCreatedInExportBibItem

Parameter	Value
Type	Modify
Location	Inside the exportBibItem() method, after the Cite object has been created
Callback arguments	cite: Cite, paperEntities: PaperEntity[]
Callback Return Value	ArgumentArray<cite: Cite, paperEntities: PaperEntity[]>

afterExportBibItem

Parameter	Value
Type	Modify
Location	At the end of the exportBibItem() method
Callback arguments	string
Callback Return Value	ArgumentArray<string>

beforeExportBibTexKey

Parameter	Value
Type	Modify
Location	At the beginning of the exportBibTexKey() method
Callback arguments	PaperEntity[]
Callback Return Value	ArgumentArray<PaperEntity[]>

citeObjCreatedInExportBibTexKey

Parameter	Value
Type	Modify
Location	Inside the exportBibTexKey() method, after the Cite object has been created
Callback arguments	cite: Cite, paperEntities: PaperEntity[]
Callback Return Value	ArgumentArray<cite: Cite, paperEntities: PaperEntity[]>

afterExportBibTexKey

Parameter	Value
Type	Modify
Location	At the end of the exportBibTexKey() method
Callback arguments	string
Callback Return Value	ArgumentArray<string>

beforeExportBibTexBody

Parameter	Value
Type	Modify
Location	At the beginning of the exportBibTexBody() method
Callback arguments	PaperEntity[]
Callback Return Value	ArgumentArray<PaperEntity[]>

citeObjCreatedInExportBibTexBody

Parameter	Value
Type	Modify
Location	Inside the exportBibTexBody() method, after the Cite object has been created
Callback arguments	cite: Cite, paperEntities: PaperEntity[]
Callback Return Value	ArgumentArray<cite: Cite, paperEntities: PaperEntity[]>

afterExportBibTexBody

Parameter	Value
Type	Modify
Location	At the end of the exportBibTexBody() method
Callback arguments	string
Callback Return Value	ArgumentArray<string>

beforeExportPlainText

Parameter	Value
Type	Modify
Location	At the beginning of the exportPlainText() method
Callback arguments	PaperEntity[]
Callback Return Value	ArgumentArray<PaperEntity[]>

citeObjCreatedInExportPlainText

Parameter	Value
Type	Modify
Location	Inside the exportPlainText() method, after the Cite object has been created
Callback arguments	cite: Cite, paperEntities: PaperEntity[]
Callback Return Value	ArgumentArray<cite: Cite, paperEntities: PaperEntity[]>

afterExportPlainText

Parameter	Value
Type	Modify
Location	At the end of the exportPlainText() method
Callback arguments	string
Callback Return Value	ArgumentArray<string>